add files to pyproject overwrite it with an invalid file

How to reproduce:

1. Create a Qt for Python - Window project
2. Go to File -> New file or project -> Python -> Python class
3. Observe that main.pyproject was edited showing only the file names in project instead of in JSON style

For example:

• After create the project you will have a main.pyproject with this content:

           { "files": ["main.py"]} 

• After you add the new python class file, the main.pyproject will have this content:

           main.pyproject

           main.py

           newclass.py

• The correct main.pyproject content would be:

           { "files": ["main.py", "newclass.py"]} 

After that your project will not run until you edit main.pyproject manually to follow JSON style again.

It occurs every time that you add a new file to project or rename an existing file.