ci: install gh CLI in release workflow for self-hosted runners

The self-hosted runner (local-ubuntu-latest) does not have gh CLI
pre-installed, causing the PR creation step to fail with
"gh: command not found" after the release is published.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/plugin-release.yaml

@@ -150,6 +150,14 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Install GitHub CLI
+        run: |
+          if ! command -v gh &>/dev/null; then
+            curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg | sudo dd of=/usr/share/keyrings/githubcli-archive-keyring.gpg
+            echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" | sudo tee /etc/apt/sources.list.d/github-cli.list > /dev/null
+            sudo apt-get update && sudo apt-get install -y gh
+          fi
+
       - name: Create PR for version bump
         run: |
           VERSION="${{ inputs.version }}"