Validate RUBYGEMS_AUTH_TOKEN in release workflow

Add a check for RUBYGEMS_AUTH_TOKEN before publishing.

Author: niwo

.github/workflows/release.yml

@@ -53,6 +53,15 @@ jobs:
           ruby-version: '3.2'
           bundler-cache: true
 
+      - name: Check if RUBYGEMS_AUTH_TOKEN is set
+        run: |
+          if [ -z "${{ secrets.RUBYGEMS_AUTH_TOKEN }}" ]; then
+            echo 'RUBYGEMS_AUTH_TOKEN not set!'
+            exit 1
+          else
+            echo 'RUBYGEMS_AUTH_TOKEN is available.'
+          fi
+
       - name: Publish gem to RubyGems
         uses: rubygems/release-gem@v2
         with: