⬇️(frontend) downgrade cunningham to 2.9.4

The last version of Cunningham has problems.
Better to downgrade to the previous version.
We add cunningham library to renovate.json
to prevent future upgrade with Renovate.
An issue will be open to upgrade to the
last version manually.

renovate.json

@@ -14,6 +14,7 @@
       "groupName": "ignored js dependencies",
       "matchManagers": ["npm"],
       "matchPackageNames": [
+        "@openfun/cunningham-react",
         "@types/react",
         "@types/react-dom",
         "eslint",