docs: update checkout action to v5 in example (#579)

Co-authored-by: Timur Olzhabayev <timur.olzhabayev@grafana.com>
Co-authored-by: Giuseppe Guerra <giuseppe.guerra@grafana.com>

Author: 3 people

README.md

@@ -84,7 +84,7 @@ jobs:
       contents: read
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: actions/setup-node@v4
         with:
           node-version: "22"