fix(api): handle partial failures in push mirror synchronization gracefully (#37782)

This MR fixes an issue in the sync push mirrors endpoint.

Previously, when triggering the synchronization of all push mirrors for
a specific repository, the entire operation would stop if a single
mirror failed for any reason. As a result, the remaining mirrors were
not processed.

With this fix, failures on individual push mirrors no longer abort the
whole synchronization process.

---------

Signed-off-by: Nicolas <bircni@icloud.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

templates/swagger/v1_json.tmpl

@@ -15646,6 +15646,9 @@
           },
           "404": {
             "$ref": "#/responses/notFound"
+          },
+          "422": {
+            "$ref": "#/responses/validationError"
           }
         }
       }

templates/swagger/v1_openapi3_json.tmpl

@@ -27446,6 +27446,9 @@
           },
           "404": {
             "$ref": "#/components/responses/notFound"
+          },
+          "422": {
+            "$ref": "#/components/responses/validationError"
           }
         },
         "summary": "Sync all push mirrored repository",