ci: bump actions/cache to v4 in pr-code-sniff.yml

actions/cache@v2 is now hard-deprecated by GitHub and fails the job at
setup, before any code even runs - unrelated to this PR's changes, but
blocking every PR's code-sniff check right now.

Author: rajatgautam755421

.github/workflows/pr-code-sniff.yml

@@ -23,7 +23,7 @@ jobs:
           composer --version
 
       - name: Get cached composer directories
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ./vendor
           key: ${{ runner.os }}-${{ hashFiles('./composer.lock') }}