Bump actions/checkout from 3 to 4 (#67)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

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

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@latest
         with:
           version: ${{ matrix.version }}

.github/workflows/docs.yml

@@ -9,7 +9,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1'

.github/workflows/formatter.yml

@@ -16,7 +16,7 @@ jobs:
         with:
           version: ${{ matrix.julia-version }}
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install JuliaFormatter and format
         # This will use the latest version by default but you can set the version like so:
         #