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-linux.yml

@@ -11,7 +11,7 @@ jobs:
         tag: [plucky, oracular, noble, jammy]
     runs-on: "ubuntu-latest"
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: recursive
     - name: Install dependencies
@@ -84,7 +84,7 @@ jobs:
         tag: [bookworm, trixie]
     runs-on: "ubuntu-latest"
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: recursive
     - name: Install dependencies

.github/workflows/build-macos.yml

@@ -16,7 +16,7 @@ jobs:
             artifact: macos-x86_64
     runs-on: ${{ matrix.runner }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: recursive
     - name: Install Qt

.github/workflows/build-windows.yml

@@ -33,7 +33,7 @@ jobs:
           #   machine: ARM64
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: recursive
     - name: Install Qt 6

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: recursive