fix: always pass server_hostname for Mumble TLS on pre-connected socket

asyncio.open_connection(sock=..., ssl=...) requires server_hostname
even when check_hostname is disabled. Pass self._host unconditionally.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/derp/mumble.py

@@ -342,9 +342,8 @@ class MumbleBot:
             ),
         )
         ssl_ctx = self._create_ssl_context()
-        hostname = self._host if self._tls_verify else None
         self._reader, self._writer = await asyncio.open_connection(
-            sock=sock, ssl=ssl_ctx, server_hostname=hostname,
+            sock=sock, ssl=ssl_ctx, server_hostname=self._host,
         )
 
     async def _send_msg(self, msg_type: int, payload: bytes = b"") -> None: