Bump actions/checkout from 3 to 4

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] <support@github.com>

.github/workflows/build_qt6.yml

@@ -75,19 +75,19 @@ jobs:
       run: choco install ninja
 
     - name: Checkout openchemistry
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: openchemistry/openchemistry
         submodules: recursive
 
     - name: Checkout avogadroapp
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: openchemistry/avogadroapp
         path: avogadroapp
 
     - name: Checkout avogadrolibs
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         path: avogadrolibs