fix(ci): skip helm-release workflow on forks

The helm-release workflow fails on forks because they don't have
a gh-pages branch set up for Helm chart publication. Add a
conditional check to only run this workflow on the upstream
nextcloud/all-in-one repository.

Fixes #8128

.github/workflows/helm-release.yml

@@ -10,6 +10,7 @@ on:
 
 jobs:
   release:
+    if: github.repository == 'nextcloud/all-in-one'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout