Don't run tests on merging master to a branch if the branch changes are non-functional

[metalwarrior665]

Related to #54

This happens when there a Readme update PR that gets stale and then requires to update to master which triggers full platform tests because master has code changes, e.g. here

[metalwarrior665]

Claude suggested to use git diff branch1...branch2 which doesn't take into account merge commits from master. I will test it out. For this to work, we will need to not have base commit which is fine, I already added excluding it for cosmetic PRs where we don't need ti anyway.

[metalwarrior665]

I have this conceptually locally, will get to it soon