Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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/dependabot-automerge.yaml

@@ -14,7 +14,7 @@ jobs:
     if: github.actor == 'dependabot[bot]'
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Get Dependabot metadata
         id: metadata

.github/workflows/rust-ci.yaml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the source code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Cache tools
         uses: actions/cache@v4
         with:
@@ -36,7 +36,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the source code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Cache tools
         uses: actions/cache@v4
         with: