test: close the loop after the network thread has completed

https://docs.python.org/3.15/library/asyncio-eventloop.html#asyncio.loop.close
reads "The loop must not be running when this function is called". It
seems safer to call `close()` after the thread has exited.

test/functional/test_framework/p2p.py

@@ -774,8 +774,8 @@ class NetworkThread(threading.Thread):
 
         self.network_event_loop.call_soon_threadsafe(self.network_event_loop.stop)
         wait_until_helper_internal(lambda: not self.network_event_loop.is_running(), timeout=timeout)
-        self.network_event_loop.close()
         self.join(timeout)
+        self.network_event_loop.close()
         # Safe to remove event loop.
         NetworkThread.network_event_loop = None