Correct path for back and restore test

There is a mismatch in path of backup folder in test and in that of
executor

Bug: 400684086
Test: com.android.providers.media.backupandrestore.BackupExecutorTest
Test: com.android.providers.media.backupandrestore.MediaBackupAgentTest
Test: com.android.providers.media.backupandrestore.RestoreExecutorTest
Flag: com.android.providers.media.flags.enable_backup_and_restore
Change-Id: I15e6721ca3cdfbce318b3d56196d500ed0285ffc
3 files changed