[automerger skipped] Add @FlakyTest annotation to LegacyProviderMigrationTest am: 7387c081c1 am: 4a5b0078ba -s ours

am skip reason: Change-Id I9a47c4928d18bfe33cd7f181bd4942e45720d7d5 with SHA-1 a63a23ec2e is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/providers/MediaProvider/+/13356025

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I5b525afcc48332fbb28f5f20d4412f67a20760e8