ci(lint): pin differential-shellcheck to v3 tag

Author: jamacku

.github/workflows/shellcheck.yml

@@ -19,7 +19,7 @@ jobs:
           fetch-depth: 0
 
       - name: Differential ShellCheck
-        uses: redhat-plumbers-in-action/differential-shellcheck@latest
+        uses: redhat-plumbers-in-action/differential-shellcheck@v3
         with:
           severity: warning
           token: ${{ secrets.GITHUB_TOKEN }}