Bump actions/checkout from 3 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
             version: '1'
             arch: x64
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         # `allow-failure` not available yet https://github.com/actions/toolkit/issues/399
         continue-on-error: ${{ matrix.julia-version == 'nightly' }}

.github/workflows/docs.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.10'