DO NOT MERGE: Timing test files
Checking how long every test file takes to run in the CI. In #26949 I'd like to run tests constraining that a whole file must be run in a single worker (so we can run `single` tests in parallel).

This means that files that will take a lot of time won't be parallelized well, and should be splitted for this to work. So, I want to know how long each takes.