Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/docs.yml

@@ -32,7 +32,7 @@ jobs:
           - release-1.14
           - release-1.13
     steps:
-      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           ref: ${{ matrix.branch }}
       - name: Set branch environment variable