Complement `TestOIDCProviderUnavailable` should use a clean deployment (cross-test pollution from modified homeserver config being re-used)

[MadLittleMods]

We enable COMPLEMENT_ENABLE_DIRTY_RUNS (docs) which means Complement will reuse deployments (shares homeservers between tests).

Because we modify the homeserver configuration in TestOIDCProviderUnavailable, this also affects all other tests that run after this test.

synapse/complement/tests/oidc_test.go

Lines 65 to 72 in c63d77a

	// Configure the OIDC Provider by writing a config fragment
	err = dockerutil.WriteFileIntoContainer(
	t,
	dc,
	deployment.ContainerID(t, "hs1"),
	"/conf/homeserver.d/oidc_provider.yaml",
	[]byte(OIDC_HOMESERVER_CONFIG),
	)

Potential solutions

As suggested in the COMPLEMENT_ENABLE_DIRTY_RUNS docs, we could use OldDeploy to get a fresh deployment. The problem is that the OldDeploy API is way more cumbersome using blueprints instead of just being able to specify the number of homeservers desired.

Ideally, we'd just be able to specify that this homeserver should not be re-used when making the deployment like deployment := complement.CleanDeploy(t, 1) (perhaps more apparent name)