Fix generate code workflow's error (#1152)

I'm not sure why, but generate-code workflow failed. This change fixes
it by using Java environment to generate code.
https://github.com/line/line-bot-sdk-java/actions/runs/6854764947/job/18638387636

Author: Yang-33

.github/workflows/generate-code.yml

@@ -15,10 +15,12 @@ jobs:
         uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Set up Python
-        uses: actions/setup-python@v4
+      - name: Set up Java
+        uses: actions/setup-java@v3
         with:
-          python-version: '3.x'
+          distribution: 'temurin'
+          java-version: 17
+          architecture: x64
       - name: Generate code
         run: |
           python generate-code.py