No need to have version_string as an argument since it's always the same (#19012)

Assuming, we're happy with
https://github.com/element-hq/synapse/pull/19011, this PR makes sense.

tests/server.py

@@ -1198,7 +1198,6 @@ def setup_test_homeserver(
     hs = homeserver_to_use(
         server_name,
         config=config,
-        version_string="Synapse/tests",
         reactor=reactor,
     )
 

tests/test_server.py

@@ -236,17 +236,17 @@ class OptionsResourceTests(unittest.TestCase):
         """Create a request from the method/path and return a channel with the response."""
         # Create a site and query for the resource.
         site = SynapseSite(
-            "test",
-            "site_tag",
-            parse_listener_def(
+            logger_name="test",
+            site_tag="site_tag",
+            config=parse_listener_def(
                 0,
                 {
                     "type": "http",
                     "port": 0,
                 },
             ),
-            self.resource,
-            "1.0",
+            resource=self.resource,
+            server_version_string="1",
             max_request_body_size=4096,
             reactor=self.reactor,
             hs=self.homeserver,