Prevent merging on EOL branches

Signed-off-by: John Molakvoæ <skjnldsv@protonmail.com>

.github/workflows/block-merge-eol.yml

@@ -0,0 +1,30 @@
+# This workflow is provided via the organization template repository
+#
+# https://github.com/nextcloud/.github
+# https://docs.github.com/en/actions/learn-github-actions/sharing-workflows-with-your-organization
+
+name: Pull request checks
+
+on: pull_request
+
+jobs:
+  block-merges-eol:
+    name: Block merges for EOL branches
+
+    # Only run on stableXX branches
+    if: startsWith( github.base_ref, 'stable')
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Download updater config
+        run: curl https://raw.githubusercontent.com/nextcloud/updater_server/production/config/config.php --output config.php
+
+      - name: Set server major version environment
+        run: |
+          # retrieve version number from branch reference
+          server_major=$(echo "${{ github.base_ref }}" | sed -En 's/stable//p')
+          echo "server_major=$server_major" >> $GITHUB_ENV
+ 
+      - name: Checking if ${{ env.server_major }} is EOL
+        run: |
+          php -r 'echo json_encode(require_once "config.php");' | jq --arg version "${{ env.server_major }}" '.stable[$version]["100"].eol' | grep --silent -i 'false'