chore(deps): bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 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/v5...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/check-formatting.yaml

@@ -9,7 +9,7 @@ jobs:
     name: Check formatting
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive
 

.github/workflows/ci.yaml

@@ -40,7 +40,7 @@ jobs:
           node-version: 24
 
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive
 
@@ -96,7 +96,7 @@ jobs:
         uses: microsoft/setup-msbuild@v2.0.0
 
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive
 

.github/workflows/release.yaml

@@ -23,7 +23,7 @@ jobs:
           update-alternatives --set g++ /usr/bin/g++-13
 
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive
 
@@ -50,7 +50,7 @@ jobs:
     runs-on: windows-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive