Merge all PRs for the subdirs into a single PR

[Red-Portal]

Hi, I currently work on some projects that have multiple subdirs that all need compat bumps. When informing CompatHelper of all these subdirs, it opens a PR for each subdir even though it is for the same compat bump. It would be great if CompatHelper could just submit one PR that would bump all of the relevant compat entries in a package-wide fashion.

[gdalle]

I just went through this with DifferentiationInterface and I got 25 PRs, each of which takes roughly one hour of CI times 20-something jobs. Long story short, I spent the power equivalent of my hometown to update compat bounds.