xmpp_cert_sync: keep Jinja out of the script's f-strings

The metric line's {{cert=...}} braces were read as a Jinja expression
and failed the template. Render only the settings, the rest verbatim.

Assisted-by: Claude:opus-5-5

ansible/roles/xmpp_cert_sync/templates/xmpp-cert-sync.j2

@@ -12,6 +12,7 @@ KEY = "/root/.ssh/xmpp_cert_sync"
 KNOWN = "/root/.ssh/xmpp_cert_sync_known_hosts"
 STATE = "/var/lib/xmpp-cert-sync"
 PROM = "{{ monitoring_textfile_dir }}/xmpp_cert.prom"
+{% raw %}
 
 
 def not_after(pem):
@@ -66,3 +67,4 @@ else:
 with open(PROM + ".tmp", "w") as f:
     f.write("\n".join(lines) + "\n")
 os.replace(PROM + ".tmp", PROM)
+{% endraw %}