Fix failing /sync tests

[matrixbot]

This issue was originally created by @kegsay at matrix-org/dendrite#1324.

They should be passing but for some reason are not.

Sytests:

    × Newly joined room has correct timeline in incremental sync
    × Newly joined room includes presence in incremental sync
    × When user joins a room the state is included in the next sync
    × When user joins a room the state is included in a gapped sync
    × When user joins and leaves a room in the same batch, the full state is still included in the next sync
    × Current state appears in timeline in private history with many messages after

[matrixbot]

This comment was originally posted by @kegsay at matrix-org/dendrite#1324 (comment).

Test 315 Newly joined room has correct timeline in incremental sync... EXPECTED FAIL
Test 316 Newly joined room includes presence in incremental sync... EXPECTED FAIL
Test 326 A next_batch token can be used in the v1 messages API... OK
Test 330 State is included in the timeline in the initial sync... OK
Test 331 State from remote users is included in the state in the initial sync... OK
Test 333 Changes to state are included in an gapped incremental sync... OK
Test 336 When user joins a room the state is included in the next sync... EXPECTED FAIL
Test 337 A change to displayname should not result in a full state sync... OK
Test 339 When user joins a room the state is included in a gapped sync... EXPECTED FAIL
Test 340 When user joins and leaves a room in the same batch, the full state is still included in the next sync... EXPECTED FAIL
Test 343 Current state appears in timeline in private history with many messages after... EXPECTED FAIL
Test 798 Multiple calls to /sync should not cause 500 errors... OK