Complement `TestDeviceListUpdates/when_remote_user_joins_a_room` flake(?)

[DMRobertson]

https://github.com/matrix-org/synapse/actions/runs/3204302461/jobs/5235520023

      client.go:604: [CSAPI] POST hs1/_matrix/client/v3/register => 200 OK (195.428656ms)
      client.go:604: [CSAPI] POST hs2/_matrix/client/v3/register => 200 OK (314.031457ms)
      client.go:604: [CSAPI] POST hs2/_matrix/client/v3/keys/upload => 200 OK (110.185852ms)
      client.go:604: [CSAPI] POST hs1/_matrix/client/v3/createRoom => 200 OK (972.145549ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (391.917818ms)
      client.go:604: [CSAPI] POST hs2/_matrix/client/v3/join/!arpRCWNVBTAxZTROZD:hs1 => 200 OK (1.511062331s)
      client.go:604: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (607.838192ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (68.691406ms)
      client.go:604: [CSAPI] POST hs1/_matrix/client/v3/keys/query => 200 OK (421.023188ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (72.393428ms)
      client.go:604: [CSAPI] POST hs2/_matrix/client/v3/keys/upload => 200 OK (95.074462ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (25.043548ms)
      client.go:604: [CSAPI] POST hs1/_matrix/client/v3/keys/query => 200 OK (57.322639ms)
      device_lists_test.go:139: MatchResponse key 'device_keys.@bob4:hs2.ZJUCSAPZAX.keys.ed25519:ZJUCSAPZAX' got 'PbiLbZNrfrWbmKA7kCBEhJJ0GCXy+1TElIftsHrUq/k' want 'vxjhBYRfe3Q5xzOtu4i1BBX2fNtOcCPfmDp5Fhz7Nh0' - http://localhost:49456/_matrix/client/v3/keys/query => {"device_keys":{"@bob4:hs2":{"ZJUCSAPZAX":{"algorithms":["m.olm.v1.curve25519-aes-sha2","m.megolm.v1.aes-sha2"],"device_id":"ZJUCSAPZAX","keys":{"curve25519:ZJUCSAPZAX":"L++DP/WvCewd4aygNB0hNiMxyz0SH+ervHL0zadrGg4","ed25519:ZJUCSAPZAX":"PbiLbZNrfrWbmKA7kCBEhJJ0GCXy+1TElIftsHrUq/k"},"user_id":"@bob4:hs2","unsigned":{}}}},"failures":{},"master_keys":{},"self_signing_keys":{},"user_signing_keys":{}}

Very possibly covered by another issue. Sorry for noise if so.

[squahtx]

todo: figure out whether this has the same cause as matrix-org/complement#580

[DMRobertson]

https://github.com/matrix-org/synapse/actions/runs/3240366604/jobs/5310901148

[DMRobertson]

https://github.com/matrix-org/synapse/actions/runs/3271906848/jobs/5382322189

[anoadragon453]

https://github.com/matrix-org/synapse/actions/runs/3273699374/jobs/5386495549#step:6:8948

[DMRobertson]

https://github.com/matrix-org/synapse/actions/runs/3344502928/jobs/5538985711

[DMRobertson]

https://github.com/matrix-org/synapse/actions/runs/3345579439/jobs/5541353861