Flaky tests: TestOverlayDiffApply10Files, TestOverlayChanges (ARM)

[thaJeztah]

These test were failing on ARM, possibly due to it being slower than other builds. They were disabled in #23501, but opening this to keep track (so that we can update them to fix)

/cc @dmcgowan

05:33:11 --- FAIL: TestOverlayDiffApply10Files (0.25s)
05:33:11    graphtest_unix.go:249: Apply diff size different, got 576, expected 640
05:33:11 --- FAIL: TestOverlayChanges (0.12s)
05:33:11    graphtest_unix.go:286: unexpected number of changes, expected 21, got 16