Demote unstable tests (#29250)

* [skip ci] Demote unstable tests
* [skip ci] Further demotions, fix artifact jumbling

e2e-tests/cypress/tests/integration/channels/notifications/ignore_channel_mentions_spec.js

@@ -7,7 +7,6 @@
 // - Use element ID when selecting an element. Create one if none.
 // ***************************************************************
 
-// Stage: @prod
 // Group: @channels @notifications
 
 import * as TIMEOUTS from '../../../fixtures/timeouts';