Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...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>

.github/workflows/build-onpremise.yml

@@ -35,7 +35,7 @@ jobs:
 
     steps:
       - name: "Check out code"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0 # Required for WyriHaximus/github-action-get-previous-tag
 
@@ -96,7 +96,7 @@ jobs:
           node-version: '20.x'
 
       - name: "Checkout invoicing extension"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: solidtime-io/extension-invoicing
           path: extensions/Invoicing