Only run proposed runs if a file diff from main

When you’re working on a branch and push a change to a file, it’ll trigger all the stacks that have that file configured as an additional glob.

The big issue appears when that branch gets updated with the main branch via merge commit. This could result in as many proposed runs as files changed in main, that have nothing shared with the working branch.

I think that, for proposed runs, a diff should be performed with main, and if there’s no changes, the run shouldn’t be triggered. This would prevent many useless runs and would drastically reduce the amount of work and time that the workers have to manage.