Bump actions/checkout from 6 to 7 (#181)

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -54,7 +54,7 @@ jobs:
           - {backend: blas64, julia-version: 'nightly'}
           - {backend: accelerate, julia-version: 'nightly'}
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - uses: julia-actions/setup-julia@v3
         with:
@@ -114,7 +114,7 @@ jobs:
           # Only the core `openblas` and `direct` backends run on nightly.
           - {backend: refblas, julia-version: 'nightly'}
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - uses: julia-actions/setup-julia@v3
         with:
@@ -160,7 +160,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - name: Regenerate func_list and check for diff
         run: |
           cd ext/gensymbol