Use the latest submodules when generating code is hooked (#1232)

When we run `generate-code.yml` manually, this doesn't generated code
when it's before line-openapi is not updated yet.
This change fixes it. Note line-bot-sdk-php and line-bot-sdk-go do this.
(python, java, and nodejs don't do this yet)

Author: Yang-33

.github/workflows/generate-code.yml

@@ -15,6 +15,8 @@ jobs:
         uses: actions/checkout@v4
         with:
           submodules: recursive
+      - name: Update submodules
+        run: git submodule update --remote --recursive
       - name: Set up Java
         uses: actions/setup-java@v4
         with: