[MachinePipeliner] Fix scheduling-sensitive tests

There are tests that are more sensitive to scheduling results than
necessary. For example, a test that is intended to verify the
correctness of the dependency analysis but is validating the final
scheduling results These tests can be affected by unrelated changes.
This patch fixes them to make them robust against such changes. This
patch is a prelude to llvm#121907.

Author: kasuga-fj