Skip creating PR when only git submodule is updated (#784)

same as line/line-bot-sdk-nodejs#1210

Author: Yang-33

.github/workflows/generate-code.yml

@@ -21,15 +21,16 @@ jobs:
       - name: Update submodules
         run: git submodule update --remote --recursive
       - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
-      - name: Set up Python
-        uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
-        with:
-          python-version: '3.x'
       - name: Generate code
-        run: |
-          python generate-code.py
-          diff=$(git --no-pager diff --name-only HEAD)
-          echo "DIFF_IS_EMPTY=$([[ -z "$diff" ]] && echo 'true' || echo 'false')" >> $GITHUB_ENV
+        run: python generate-code.py
+      - run: |
+          diff_files=$(git --no-pager diff --name-only)
+          diff_excluding_submodule=$(echo "$diff_files" | grep -v '^line-openapi$' || true)
+
+          echo "diff files: $diff_files"
+          echo "diff excluding submodule: $diff_excluding_submodule"
+
+          echo "DIFF_IS_EMPTY=$([[ -z "$diff_excluding_submodule" ]] && echo 'true' || echo 'false')" >> $GITHUB_ENV
           echo "CURRENT_DATETIME=$(date +'%Y%m%d%H%M%S')" >> $GITHUB_ENV
       ## Run if diff exists and pull request, and make CI status failure (but allow renovate bot)
       - if: ${{ github.event_name == 'pull_request' && env.DIFF_IS_EMPTY != 'true' && github.actor != 'renovate[bot]' }}