Fix missing "stun:" prefix for jitsi/web STUN server URLs

Hopefully fixes an error like this (which I haven't been able to
reproduce, but..):

> [modules/xmpp/strophe.util.js] <Object.i.Strophe.log>:  Strophe: Error: Failed to construct 'RTCPeerConnection': 'matrix.DOMAIN' is not one of the supported URL schemes 'stun', 'turn' or 'turns'.

group_vars/matrix_servers

@@ -412,11 +412,11 @@ matrix_jitsi_jvb_auth_password: "{{ matrix_synapse_macaroon_secret_key | passwor
 matrix_jitsi_web_stun_servers: |
   {{
     [
-      matrix_server_fqn_matrix + ':5349',
+      'stun:' + matrix_server_fqn_matrix + ':5349',
-      matrix_server_fqn_matrix + ':3478',
+      'stun:' + matrix_server_fqn_matrix + ':3478',
     ]
     if matrix_coturn_enabled
-    else [ 'meet-jit-si-turnrelay.jitsi.net:443']
+    else [ 'stun:meet-jit-si-turnrelay.jitsi.net:443']
   }}
 
 ######################################################################

roles/matrix-jitsi/defaults/main.yml

@@ -38,7 +38,8 @@ matrix_jitsi_web_transcripts_path: "{{ matrix_jitsi_web_base_path }}/transcripts
 matrix_jitsi_web_public_url: "https://{{ matrix_server_fqn_jitsi }}"
 
 # STUN servers used in the web UI. Feel free to point them to your own STUN server.
-matrix_jitsi_web_stun_servers: ['meet-jit-si-turnrelay.jitsi.net:443']
+# Addresses need to be prefixed with one of `stun:`, `turn:` or `turns:`.
+matrix_jitsi_web_stun_servers: ['stun:meet-jit-si-turnrelay.jitsi.net:443']
 
 # Controls whether the matrix-jitsi-web container exposes its HTTP port (tcp/80 in the container).
 #