chore: convert dbauthz tests to also run with Postgres (#15862)

Another PR to address https://github.com/coder/coder/issues/15109.

- adds the DisableForeignKeysAndTriggers utility, which simplifies
converting tests from in-mem to postgres
- converts the dbauthz test suite to pass on both the in-mem db and
Postgres

coderd/database/dbmem/dbmem.go

@@ -2206,6 +2206,11 @@ func (q *FakeQuerier) DeleteWorkspaceAgentPortSharesByTemplate(_ context.Context
 	return nil
 }
 
+func (*FakeQuerier) DisableForeignKeysAndTriggers(_ context.Context) error {
+	// This is a no-op in the in-memory database.
+	return nil
+}
+
 func (q *FakeQuerier) EnqueueNotificationMessage(_ context.Context, arg database.EnqueueNotificationMessageParams) error {
 	err := validateDatabaseType(arg)
 	if err != nil {