Upgrade action checkout

Author: dontcallmedom

.github/workflows/auto-publish.yml

@@ -11,7 +11,7 @@ jobs:
     name: Validate and Publish
     runs-on: ubuntu-20.04 # only linux supported at present
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: w3c/spec-prod@v2 # use the action
         with:
           W3C_WG_DECISION_URL: "https://lists.w3.org/Archives/Public/public-webrtc/2016Mar/0031.html"