Bump actions/checkout in the actions-updates group

Bumps the actions-updates group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 6.pre.beta to 6.0.0
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@71cf226...1af3b93)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 6.0.0
  dependency-type: direct:production
  dependency-group: actions-updates
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/buf-ci.yaml

@@ -11,7 +11,7 @@ jobs:
   buf:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@71cf2267d89c5cb81562390fa70a37fa40b1305e # v4.2.0
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v4.2.0
       - uses: bufbuild/buf-action@8f4a1456a0ab6a1eb80ba68e53832e6fcfacc16c # v1.3.0
         with:
           # Publishing schema changes to the BSR requires a BSR authentication token.