ci/cd: upgrade actions to v4 to avoid NodeJS warning

Change description:

- Upgrade actions/checkout from v2 to v4
- Addresses the warnings caused by NodeJS 12 deprecation in
  actions/checkout
- actions/checkout v4 uses NodeJS 16

Signed-off-by: Maharshi Basu <[email protected]>

.github/workflows/unicode-check.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Check for unicode in sail files
         run: |