github: [skip ci]: bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/rpm-builder.yaml

@@ -116,7 +116,7 @@ jobs:
         password: ${{ secrets.REDHAT_REGISTRY_TOKEN }}
 
     - name: checkout sources
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: print commit info
       id: init