Complement flake(?) `TestPartialStateJoin/*` due to complement hostname:port re-use

[DMRobertson]

• TestPartialStateJoin/Outgoing_device_list_updates/Device_list_updates_reach_incorrectly_kicked_servers_once_partial_state_join_completes
  https://github.com/matrix-org/synapse/actions/runs/3154756275/jobs/5132733882

  federation_room_join_partial_state_test.go:1763: MustSendTransaction: contents=[123 34 101 114 114 99 111 100 101 34 58 34 77 95 85 78 65 85 84 72 79 82 73 90 69 68 34 44 34 101 114 114 111 114 34 58 34 73 110 118 97 108 105 100 32 115 105 103 110 97 116 117 114 101 32 102 111 114 32 115 101 114 118 101 114 32 104 111 115 116 46 100 111 99 107 101 114 46 105 110 116 101 114 110 97 108 58 52 52 54 57 55 32 119 105 116 104 32 107 101 121 32 101 100 50 53 53 49 57 58 99 111 109 112 108 101 109 101 110 116 58 32 85 110 97 98 108 101 32 116 111 32 118 101 114 105 102 121 32 115 105 103 110 97 116 117 114 101 32 102 111 114 32 104 111 115 116 46 100 111 99 107 101 114 46 105 110 116 101 114 110 97 108 58 52 52 54 57 55 58 32 60 99 108 97 115 115 32 39 110 97 99 108 46 101 120 99 101 112 116 105 111 110 115 46 66 97 100 83 105 103 110 97 116 117 114 101 69 114 114 111 114 39 62 32 83 105 103 110 97 116 117 114 101 32 119 97 115 32 102 111 114 103 101 100 32 111 114 32 99 111 114 114 117 112 116 34 125] msg=Failed to PUT JSON (hostname "hs1" path "/_matrix/federation/v1/send/complement-879472265") code=401 wrapped=M_UNAUTHORIZED: Invalid signature for server host.docker.internal:44697 with key ed25519:complement: Unable to verify signature for host.docker.internal:44697: <class 'nacl.exceptions.BadSignatureError'> Signature was forged or corrupt
  

• TestPartialStateJoin/CanReceiveEventsWithHalfMissingGrandparentsDuringPartialStateJoin
  https://github.com/matrix-org/synapse/actions/runs/3182363321/jobs/5188328245

      client.go:604: [CSAPI] POST hs1/_matrix/client/v3/register => 200 OK (26.184393ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (28.239677ms)
      client.go:604: [CSAPI] GET hs1/_matrix/client/v3/capabilities => 200 OK (3.172875ms)
      server.go:165: Creating room !0:host.docker.internal:37495 with version 9
      federation_room_join_partial_state_test.go:2705: Registered state_ids handler for event $GzPAiiM7ueWOyydmKHb4tyYhwmXXS0iOBtzWJZDYxkE
      federation_room_join_partial_state_test.go:2746: Registered /state handler for event $GzPAiiM7ueWOyydmKHb4tyYhwmXXS0iOBtzWJZDYxkE
      client.go:602: [CSAPI] POST hs1/_matrix/client/v3/join/!0:host.docker.internal:37495 => error: net/http: request canceled (30.000242265s)
      federation_room_join_partial_state_test.go:2617: CSAPI.DoFunc response returned error: Post "http://localhost:49288/_matrix/client/v3/join/%210:host.docker.internal:37495?server_name=host.docker.internal%3A37495": net/http: request canceled (Client.Timeout exceeded while awaiting headers)
  

[squahtx]

It's failing with
federation_room_join_partial_state_test.go:1763: MustSendTransaction: contents=[123 34 101 114 114 99 111 100 101 34 58 34 77 95 85 78 65 85 84 72 79 82 73 90 69 68 34 44 34 101 114 114 111 114 34 58 34 73 110 118 97 108 105 100 32 115 105 103 110 97 116 117 114 101 32 102 111 114 32 115 101 114 118 101 114 32 104 111 115 116 46 100 111 99 107 101 114 46 105 110 116 101 114 110 97 108 58 52 52 54 57 55 32 119 105 116 104 32 107 101 121 32 101 100 50 53 53 49 57 58 99 111 109 112 108 101 109 101 110 116 58 32 85 110 97 98 108 101 32 116 111 32 118 101 114 105 102 121 32 115 105 103 110 97 116 117 114 101 32 102 111 114 32 104 111 115 116 46 100 111 99 107 101 114 46 105 110 116 101 114 110 97 108 58 52 52 54 57 55 58 32 60 99 108 97 115 115 32 39 110 97 99 108 46 101 120 99 101 112 116 105 111 110 115 46 66 97 100 83 105 103 110 97 116 117 114 101 69 114 114 111 114 39 62 32 83 105 103 110 97 116 117 114 101 32 119 97 115 32 102 111 114 103 101 100 32 111 114 32 99 111 114 114 117 112 116 34 125] msg=Failed to PUT JSON (hostname "hs1" path "/_matrix/federation/v1/send/complement-879472265") code=401 wrapped=M_UNAUTHORIZED: Invalid signature for server host.docker.internal:44697 with key ed25519:complement: Unable to verify signature for host.docker.internal:44697: <class 'nacl.exceptions.BadSignatureError'> Signature was forged or corrupt

which might be due to the way we re-use the same Synapse deployment, but spin complement homeservers up and down across multiple tests. Each time we spin a complement homeserver up, it probably ends up with a different key. And when we have a complement server that reuses the port (and hostname) of a previous one, I'd expect the tests to fail.

[squahtx]

matrix-org/complement#486 may not be sufficient, since it only handles homeserver keys.
We still end up re-using room IDs across tests which is going to break things.