CI loops

Stream: mathlib4

[Floris van Doorn]

The CI for this commit seems to have reached an infinite loop:
https://github.com/leanprover-community/mathlib4/actions/runs/4438073239/jobs/7788631506
It printed the message

Warning: ./Mathlib/Lean/Linter.lean not found. Skipping all files that depend on it

more than 30k times, and ran for more than 5 hours.
I made a mistake with that commit, forgetting to commit/push the file Mathlib/Lean/Linter.lean and also forgetting to include it in Mathlib.lean, but that should cause the CI to fail gracefully.