Make provenance heading conditional (#17077)

Author: di

warehouse/templates/includes/file-details.html

@@ -97,9 +97,8 @@ <h3>File hashes</h3>
     </p>
   </div>
 
-  <h3>Provenance</h3>
-
   {% if file.provenance %}
+  <h3>Provenance</h3>
     {% set provenance = file.provenance.as_model %}
     <p>
     The following attestation bundles were made for <code>{{ file.filename }}</code>: