CI: Bump actions/checkout from 4.2.2 to 5.0.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 4.2.2 to 5.0.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4.2.2...08c6903)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 5.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/extension-validation.yml

@@ -19,7 +19,7 @@ jobs:
       pull-requests: write
     timeout-minutes: 30
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
           fetch-depth: 0 # Fetch full history for git diff