Add Flaky annotation to 4 flaky tests in VibratorManagerServiceTest

Added @Flaky to:
1. onExternalVibration_withNewSameImportanceButRepeating_cancelsOngoingVibration
2. vibrate_withOngoingRepeatingVibration_ignoresEffect
3. vibrate_withNewSameImportanceVibrationButOngoingIsRepeating_ignoreNewVibration
4. vibrate_withNewUnknownUsageVibrationAndNotRepeating_ignoreNewVibration

onExternalVibration_withNewSameImportanceButRepeating_cancelsOngoingVibration's
failures were blocking presubmit.

Bug: 299481519
Test: N/A
Change-Id: If7c7a2c94db3eac4f4bc79a6c05c35683031a50c