webrtc: Reset received_caps when releasing pad

This is to work around a race where the pad is accessed in the
webrtc main thread while being released.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2104>

ext/webrtc/gstwebrtcbin.c

@@ -6268,6 +6268,7 @@ gst_webrtc_bin_release_pad (GstElement * element, GstPad * pad)
   if (webrtc_pad->trans)
     gst_object_unref (webrtc_pad->trans);
   webrtc_pad->trans = NULL;
+  gst_caps_replace (&webrtc_pad->received_caps, NULL);
   PC_UNLOCK (webrtc);
 
   _remove_pad (webrtc, webrtc_pad);