Try to make Jinja not trip up over syntax

roles/matrix-bridge-mautrix-whatsapp/templates/config.yaml.j2

@@ -80,7 +80,7 @@ whatsapp:
 # Bridge config
 bridge:
     # Localpart template of MXIDs for WhatsApp users.
-    # {{.}} is replaced with the phone number of the WhatsApp user.
+    # {% raw %}{{.}}{% endraw %} is replaced with the phone number of the WhatsApp user.
     username_template: "{{ 'whatsapp_{{.}}' }}"
     # Displayname template for WhatsApp users.
     # {{.PushName}}     - nickname set by the WhatsApp user