[wptrunner] Optimize server test order (#46331)

`TestEnvironment.ensure_started()` synchronously polls that all servers
are started. The non-webtransport-h3 servers are often tested first and
immediately fail with "Connection refused", which puts them in the
`pending` list. This spins the polling loop at least once and delays
startup by at least 0.5s.

Run the webtransport-h3 server test first, which blocks [1]. This
provides additional time for the non-webtransport-h3 servers to become
ready, which means the `TestEnvironment` often only needs to poll once.

This speeds up `ensure_started()` from ~2.2s -> ~1.7s and improves
wptrunner's interactive UX (https://crbug.com/339299999). No functional
change.

[1]: https://github.com/web-platform-tests/wpt/blob/431f8d35/tools/webtransport/h3/webtransport_h3_server.py#L593

tools/wptrunner/wptrunner/environment.py

@@ -291,12 +291,18 @@ def test_servers(self):
                     failed.append((scheme, port))
 
         if not failed and self.test_server_port:
+            # The webtransport-h3 server test blocks (i.e., doesn't fail quickly
+            # with "Connection refused" like the sockets do), so testing these
+            # first improves the likelihood the non-webtransport-h3 servers are
+            # ready by the time they're checked.
+            for port, server in self.servers.get("webtransport-h3", []):
+                if not webtranport_h3_server_is_running(host, port, timeout=5):
+                    pending.append((host, port))
+
             for scheme, servers in self.servers.items():
+                if scheme == "webtransport-h3":
+                    continue
                 for port, server in servers:
-                    if scheme == "webtransport-h3":
-                        if not webtranport_h3_server_is_running(host, port, timeout=5.0):
-                            pending.append((host, port))
-                        continue
                     s = socket.socket()
                     s.settimeout(0.1)
                     try: