Speed up testing by automatically passing if certain files don't change

[f0uriest]

We talked about this before and in general it's tricky, but I think we can add a few simple cases:

• if nothing in desc or tests changes then unit and regression tests aren't needed
• if nothing in docs/notebooks or desc or tests changes then notebook tests aren't needed
• if nothing in desc or tests/benchmarks changes then benchmarks aren't needed

[unalmis]

Might be nice to also have a run_all_tests label that we can use to override the heuristics given above

[YigitElma]

What if we change dependencies? That requires the whole test to run. I thought about this kind of check before but I think the best we can do is skipping notebook tests if nothing in docs/notebooks, desc or requirements changed. And also we can skip all tests except notebook ones, if the only change is in docs/notebooks.

[YigitElma]

So, I think the number of PR's that would benefit this kind of change is really low. But I can look into it

[YigitElma]

#1235 (comment)