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/buildtest.yml

@@ -47,7 +47,7 @@ jobs:
         sudo rm -rf /usr/share/swift
 
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3
@@ -81,7 +81,7 @@ jobs:
         sudo rm -rf /usr/share/swift
 
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3
@@ -115,7 +115,7 @@ jobs:
         sudo rm -rf /usr/share/swift
 
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3

.github/workflows/release.yml

@@ -29,7 +29,7 @@ jobs:
         df -h
 
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3