Fix notification channel creation for screen recording

Attempt to create a channel each time before posting a notification to make sure it's there.

Flag: com.android.systemui.thin_screen_recording_service
Bug: 368579013
Test: manually on foldable. Make sure notification always appears when the recording is active.
Change-Id: I748c8da5a35e08611a189d63358b98b2725dbdfe