Fix unique_user_filter_index schema update

[babolivier]

Fixes a bug introduced in #1172

Fixes a syntax error in the ALTER TABLE statement (each ALTER COLUMN line must end with a comma, see https://www.postgresql.org/docs/9.6/sql-altertable.html).

[babolivier]

For context, this bug killed my homeserver:

synapse[31398]: 2019-10-07 12:03:48,690 - root - 236 - WARNING - None- ***** STARTING SERVER *****
synapse[31398]: 2019-10-07 12:03:48,690 - root - 237 - WARNING - None- Server /home/synapse/synapse/synapse/app/homeserver.py version 1.4.0 (b=develop,ae0b78cb1)
synapse[31398]: 2019-10-07 12:03:48,691 - root - 238 - INFO - None- Server hostname: abolivier.bzh
synapse[31398]: 2019-10-07 12:03:48,692 - synapse.app.homeserver - 359 - INFO - None- Preparing database: psycopg2...
synapse[31398]: 2019-10-07 12:03:48,890 - synapse.storage.prepare_database - 249 - INFO - None- Upgrading schema to v56
synapse[31398]: 2019-10-07 12:03:48,894 - synapse.storage.prepare_database - 276 - INFO - None- Running script 56/unique_user_filter_index.py
synapse[31398]: 2019-10-07 12:03:48,896 - twisted - 171 - ERROR - - Traceback (most recent call last):
synapse[31398]: 2019-10-07 12:03:48,897 - twisted - 171 - ERROR - -   File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
synapse[31398]: 2019-10-07 12:03:48,898 - twisted - 171 - ERROR - -     "__main__", mod_spec)
synapse[31398]: 2019-10-07 12:03:48,899 - twisted - 171 - ERROR - -   File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
synapse[31398]: 2019-10-07 12:03:48,899 - twisted - 171 - ERROR - -     exec(code, run_globals)
synapse[31398]: 2019-10-07 12:03:48,900 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/app/homeserver.py", line 659, in <module>
synapse[31398]: 2019-10-07 12:03:48,901 - twisted - 171 - ERROR - -     main()
synapse[31398]: 2019-10-07 12:03:48,902 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/app/homeserver.py", line 654, in main
synapse[31398]: 2019-10-07 12:03:48,903 - twisted - 171 - ERROR - -     hs = setup(sys.argv[1:])
synapse[31398]: 2019-10-07 12:03:48,903 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/app/homeserver.py", line 363, in setup
synapse[31398]: 2019-10-07 12:03:48,904 - twisted - 171 - ERROR - -     prepare_database(db_conn, database_engine, config=config)
synapse[31398]: 2019-10-07 12:03:48,904 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/storage/prepare_database.py", line 71, in prepare_database
synapse[31398]: 2019-10-07 12:03:48,905 - twisted - 171 - ERROR - -     cur, user_version, delta_files, upgraded, database_engine, config
synapse[31398]: 2019-10-07 12:03:48,906 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/storage/prepare_database.py", line 279, in _upgrade_existing_database
synapse[31398]: 2019-10-07 12:03:48,906 - twisted - 171 - ERROR - -     module.run_upgrade(cur, database_engine, config=config)
synapse[31398]: 2019-10-07 12:03:48,907 - twisted - 171 - ERROR - -   File "/home/synapse/synapse/synapse/storage/schema/delta/56/unique_user_filter_index.py", line 40, in run_upgrade
synapse[31398]: 2019-10-07 12:03:48,907 - twisted - 171 - ERROR - -     cur.execute(sql)
synapse[31398]: 2019-10-07 12:03:48,908 - twisted - 171 - ERROR - - psycopg2.errors.SyntaxError: syntax error at or near "ALTER"
synapse[31398]: 2019-10-07 12:03:48,908 - twisted - 171 - ERROR - - LINE 12:                ALTER COLUMN filter_id SET NOT NULL
synapse[31398]: 2019-10-07 12:03:48,909 - twisted - 171 - ERROR - -                         ^
synapse[31398]: 2019-10-07 12:03:48,909 - twisted - 171 - ERROR - -
systemd[1]: synapse.service: Main process exited, code=exited, status=1/FAILURE
systemd[1]: synapse.service: Failed with result 'exit-code'.

Running this fixed SQL manually on my postgres DB passed with no syntax error. No idea why it hasn't been picked up by CI.

[anoadragon453]

LGTM!