Revert "[ci] fix determine_tests_to_run.py by finding merge base (#26790)" (#26799)
Revert "[ci] fix determine_tests_to_run.py by finding merge base (#26790)" (#26799)

This reverts commit 7cf4f8e069dc684548b60b2cc47c04a38cb03d97.
ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray,ray-project/ray