TestWebChannel::testAsyncObject() is flaky and crashes on many platforms

agent:2019/12/11 23:42:41 build.go:220: Mingw32-make[2]: Leaving directory 'C:/Users/qt/work/qt/qtwebchannel/tests/auto/qml'
agent:2019/12/11 23:42:41 build.go:220: Mingw32-make[1]: Leaving directory 'C:/Users/qt/work/qt/qtwebchannel/tests/auto'
agent:2019/12/11 23:42:41 build.go:751: 
agent:2019/12/11 23:42:41 build.go:484: Executing instruction 24 of 32 - SetExecutionPhaseName
agent:2019/12/11 23:42:41 build.go:751: 
agent:2019/12/11 23:42:41 build.go:484: Executing instruction 25 of 32 - ScheduleUploadTestResults
agent:2019/12/11 23:42:41 build.go:751: 
agent:2019/12/11 23:42:41 build.go:484: Executing instruction 26 of 32 - SetExecutionPhaseName
agent:2019/12/11 23:42:41 build.go:751: 
agent:2019/12/11 23:42:41 build.go:484: Executing instruction 27 of 32 - RunQtUnitTest
agent:2019/12/11 23:42:41 build.go:600: Running tests in directory C:/Users/qt/work/qt/qtwebchannel/tests/auto/webchannel
agent:2019/12/11 23:42:41 runner.go:72: Generating test results with TESTARGS=-o C:\Users\qt\work\testresults\tests\auto\webchannel226142103,xml -o -,txt
agent:2019/12/11 23:42:41 build.go:329: [Mingw32-make check] 900 900
agent:2019/12/11 23:42:42 build.go:220: call C:\Users\qt\work\qt\qtwebchannel\tests\auto\webchannel\target_wrapper.bat  tst_webchannel.exe -o C:\Users\qt\work\testresults\tests\auto\webchannel226142103,xml -o -,txt
agent:2019/12/11 23:42:42 build.go:220: ********* Start testing of TestWebChannel *********
agent:2019/12/11 23:42:42 build.go:220: Config: Using QtTest library 5.15.0, Qt 5.15.0 (i386-little_endian-ilp32 shared (dynamic) release build; by GCC 7.3.0)
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::initTestCase()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testRegisterObjects()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testDeregisterObjects()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testDeregisterObjectAtStart()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testInfoForObject()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testInvokeMethodConversion()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testFunctionOverloading()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testSetPropertyConversion()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testInvokeMethodOverloadResolution()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testDisconnect()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testWrapRegisteredObject()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testUnwrapObject()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testTransportWrapObjectProperties()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testRemoveUnusedTransports()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testPassWrappedObjectBack()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testWrapValues()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testWrapObjectWithMultipleTransports()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testJsonToVariant()
agent:2019/12/11 23:42:42 build.go:220: PASS   : TestWebChannel::testInfiniteRecursion()
agent:2019/12/11 23:42:42 build.go:220: A crash occurred in C:\Users\qt\work\qt\qtwebchannel\tests\auto\webchannel\tst_webchannel.exe.
agent:2019/12/11 23:42:42 build.go:220: Function time: 5ms Total time: 19ms
agent:2019/12/11 23:42:42 build.go:220: 
agent:2019/12/11 23:42:42 build.go:220: Exception address: 0x6a20dcdb
agent:2019/12/11 23:42:42 build.go:220: Exception code   : 0xc0000005
agent:2019/12/11 23:42:42 build.go:220: Nearby symbol    : ZN22QQmlWebChannelAttached11qt_metacallEN11QMetaObject4CallEiPPv
agent:2019/12/11 23:42:42 build.go:220: 
agent:2019/12/11 23:42:42 build.go:220: Stack:
agent:2019/12/11 23:42:42 build.go:220: #  1: ZN5QTest15toPrettyUnicodeEPKti() - 0x6efc26d0
agent:2019/12/11 23:42:42 build.go:220: #  2: UnhandledExceptionFilter() - 0x774408c1
agent:2019/12/11 23:42:42 build.go:220: #  3: EtwReplyNotification() - 0x77ab75d4
agent:2019/12/11 23:42:42 build.go:220: #  4: RtlInitializeExceptionChain() - 0x77aa358b
agent:2019/12/11 23:42:42 build.go:220: 
agent:2019/12/11 23:42:42 build.go:220: Mingw32-make: *** [Makefile:310: check] Error -1073741819
agent:2019/12/11 23:42:42 build.go:253: Process finished with error: exit status 2
agent:2019/12/11 23:42:42 build.go:223: Error reading from stdout/err: exit status 2
agent:2019/12/11 23:42:42 build.go:471: Executing scheduled instruction 1 of 2 - Upload all core dumps if there are some
agent:2019/12/11 23:42:42 build.go:384: Skip uploading core files because CORE_FILES_PATH is not set in the environment
agent:2019/12/11 23:42:42 build.go:473: 
agent:2019/12/11 23:42:42 build.go:471: Executing scheduled instruction 2 of 2 - Upload test results
agent:2019/12/11 23:42:42 storageclient.go:451: Collecting test results, archiving and uploading them
agent:2019/12/11 23:42:42 result.go:177: Collecting 1 test results ...
agent:2019/12/11 23:42:42 build.go:473: 
agent:2019/12/11 23:42:42 agent.go:272: Test failed
agent:2019/12/11 23:42:42 agent.go:200: ERROR building: error unmarshalling testlib xml output ('C:\Users\qt\work\testresults\tests\auto\webchannel226142103'): 'XML syntax error on line 85: unexpected EOF'.