Update tests to allow x-signing key upload without UIA #706

Job	Run time
Dendrite: SQLite	5m 0s
Dendrite: Postgres	6m 42s
Synapse: Py 3.8, SQLite 3.31.1, Monolith	8m 2s
Synapse: Py 3.8, PG 12, Monolith	9m 35s
Synapse: Py 3.8, PG 12, Workers	13m 27s
Synapse: Py 3.10, PG 14, Monolith	14m 17s
Synapse: Py 3.10, PG 14, Workers	17m 54s
Synapse: debian-testing, Monolith	10m 52s
Synapse: debian-testing, Workers	14m 15s
	1h 40m 4s

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