ci(release): honor [skip-release] marker in tag annotation

Tags annotated with [skip-release] in their message are created
without a GitHub Release. Useful for state-marker tags that should
not be announced as a release.

Example:
  git tag -a v0.1.0-alpha -m 'Release v0.1.0-alpha [skip-release]'

.github/workflows/release.yml

@@ -30,7 +30,20 @@ jobs:
           fi
           echo "VERSION=$file_version OK"
 
+      - name: Check skip-release marker
+        id: skip
+        run: |
+          msg=$(git for-each-ref "refs/tags/${GITHUB_REF_NAME}" --format='%(contents:subject)')
+          if echo "$msg" | grep -q '\[skip-release\]'; then
+            echo "skip=true (tag message contains [skip-release])"
+            echo "skip=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "skip=false"
+            echo "skip=false" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Create GitHub release
+        if: steps.skip.outputs.skip != 'true'
         uses: softprops/action-gh-release@v2
         with:
           tag_name: ${{ github.ref_name }}