ci: Run workflows only if changes involves them

[FBruzzesi]

Description

Followup on #3609 (comment)

Trying to follow the same polars philosophy:

Only run checks when they need to be run

---

Difference between src/** and **.py case is to distinguish between:

• Something changed in the source code that we ship, then we should run all downstream deps
• Any python file changes (e.g. tpch, test-plugin, etc), then our test suite should run

What type of PR is this? (check all applicable)

• 💾 Refactor
• ✨ Feature
• 🐛 Bug Fix
• 🔧 Optimization
• 📝 Documentation
• ✅ Test
• 🐳 Other

[dangotbanned]

@FBruzzesi If you wanna move this out of draft I'll review it.

It seems ready to me, but I don't wanna prioritize it over others that you've marked as ready 🙂

[FBruzzesi]

@dangotbanned my only concern is about the repo ruleset for merging. Since some jobs do not run, they don't show up as succeeded, therefore merging is not available. I will try to take a look at the github docs this week

[dangotbanned]

Ah I see, yeah I think changing those rules is above my pay grade sadly 😅

[FBruzzesi]

@dangotbanned according to https://docs.github.com/en/actions/how-tos/write-workflows/choose-when-workflows-run/control-jobs-with-conditions

A job that is skipped will report its status as "Success". It will not prevent a pull request from merging, even if it is a required check.

---

I think that if you/someone approves it, then it should act as any other PR

[dangotbanned]

Thanks @FBruzzesi!

I stole the self-ref idea from (https://github.com/pola-rs/polars/blob/7b05d67937a6b715a813b65a20ee8fa8a01d4950/.github/workflows/test-python.yml)