Complement Postgres & Complement workers: de-flaking

[reivilibre]

The Postgres and workers Complement runs, which have recently been enabled, are a bit flakey at times.

Let's track the list of flakey tests here and get them cleaned up.

• TestFederationRoomsInvite/Parallel/Invited_user_can_reject_invite_over_federation_for_empty_room
• TestRestrictedRoomsLocalJoinInMSC3787Room/Join_should_fail_when_left_allowed_room and TestRestrictedRoomsLocalJoin}/Join_should_fail_when_left_allowed_room: https://github.com/matrix-org/synapse/runs/7179299458?check_suite_focus=true
• TestRestrictedRoomsLocalJoin/Join_should_succeed_when_joined_to_allowed_room and TestRestrictedRoomsLocalJoinInMSC3787Room/Join_should_succeed_when_joined_to_allowed_room: https://github.com/matrix-org/synapse/runs/7179299458?check_suite_focus=true
  • Race condition where a second join races with cache invalidation over replication and erroneously rejects joining Restricted Room #13185
  • Deflake Join_should_succeed_when_joined_to_allowed_room subtest of restricted rooms tests complement#413

Once all this is done, we can close #13264.

[squahtx]

(This comment referred to an MSC3787 tests. I've moved this to the top-level one with the other restricted rooms failures, as the underlying cause is the same. -- dmr.)

[DMRobertson]

• Complement Existing members see new members' presence is flaky #13199

[DMRobertson]

• TestWriteMDirectAccountData, see Complement TestWriteMDirectAccountData is flakey #13334

[DMRobertson]

• TestSendJoinPartialStateResponse: see TestSendJoinPartialStateResponse is flaky #13256

[squahtx]

• TestSync/parallel/sync_should_succeed_even_if_the_sync_token_points_to_a_redaction_of_an_unknown_event
  • https://github.com/matrix-org/synapse/runs/7197178106?check_suite_focus=true#step:4:6887
  • https://github.com/matrix-org/synapse/runs/7435035090?check_suite_focus=true (This particular case should be solved by Fix an out of bounds error in TestSync 'sync should succeed even if the sync token points to a redaction of an unknown event' complement#427)