Actions: Bump checkout action

.github/workflows/check-submodule-pointers.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'github/vscode-codeql-starter'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Compare submodule pointers to lgtm.com branch
         env: