Bump cache action from EOL'd v2 to v4

Author: nie7321

.github/workflows/terraform-reusable.yml

@@ -52,7 +52,7 @@ jobs:
       - name: Cache Comment Id
         if: github.event_name == 'pull_request'
         id: cache-comment-id
-        uses: actions/cache@v2.1.7
+        uses: actions/cache@v4.2.3
         with:
           path: ./comment-cache
           key: pr-${{ github.event.number }}-comment-id${{ inputs.cache-key-suffix }}