Fix Jinja2 syntax error

Fixes a regression introduced in ffe649a240

roles/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -1944,8 +1944,8 @@ oidc_providers:
   #  user_mapping_provider:
   #    config:
   #      subject_claim: "id"
-  #      localpart_template: "{{ user.login }}"
-  #      display_name_template: "{{ user.name }}"
+  #      localpart_template: "{% raw %}{{ user.login }}{% endraw %}"
+  #      display_name_template: "{% raw %}{{ user.name }}{% endraw %}"
 
 
 # Enable Central Authentication Service (CAS) for registration and login.