Sanity-bot: Allow patch branches in Pick-to footer of existing cherry pick

When cherry-pick bot is enabled, sanity bot gives a -2 to any cherry-pick that contains a Pick-to footer. This is a safeguard against users manually cherry-picking and leaving a redundant Pick-To footer which would result in an erroneous pick by the Qt Cherry-pick Bot.

A shortcoming of this is that when a change is picked to a minor branch, 5.12 for example, sanity-bot will disallow a Pick-to footer which could be used to pick to the latest 5.12 patch release branch, 5.12.9 for example.

Ideally, the forward merge strategy can be dropped in all cases in favour of cherry-picking. As such, the sanity bot should allow the Pick-to footer on a cherry pick under the following condition:

• The pick exists on a minor, numbered, non-dev branch (X.XX)
• The Pick-to footer specifies only patch branches which are part of the minor branch. (X.XX.XX)