fix: Drop cache@v2 because it will break soon. (#4516)

See the announcement here: https://github.blog/changelog/2024-09-16-notice-of-upcoming-deprecations-and-changes-in-github-actions-services/

.github/workflows/migrations-check-mysql8.yml

@@ -36,7 +36,7 @@ jobs:
 
     - name: Cache pip dependencies
       id: cache-dependencies
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ${{ steps.pip-cache-dir.outputs.dir }}
         key: ${{ runner.os }}-pip-${{ hashFiles('requirements/pip_tools.txt') }}