chore(deps): update actions/checkout action to v4 (#1911)

* chore(deps): update actions/checkout action to v4

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

.github/workflows/system-tests-against-emulator.yaml

@@ -16,7 +16,7 @@ jobs:
           - 9020:9020
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - uses: actions/setup-node@v3
         with:
           node-version: 14