Give `tests.server.setup_test_homeserver` (nominally!) the same behaviour

by calling into `make_test_homeserver_synchronous`.

The function *could* have been inlined at this point but the function is big enough

and it felt fine to leave it as is.

At least there isn't a confusing name clash anymore!

tests/server.py

@@ -850,4 +850,7 @@ def setup_test_homeserver(
 
     hs.get_auth_handler().validate_hash = validate_hash
 
+    # Make the threadpool and database transactions synchronous for testing.
+    make_test_homeserver_synchronous(hs)
+
     return hs