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](actions/checkout@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] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
     runs-on: macOS-13
     steps:
       - name: git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: unit tests
         run: |

.github/workflows/pod-lint.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: macOS-13
     steps:
       - name: git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: ruby versions
         run: |

.github/workflows/spm.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: macOS-13
     steps:
       - name: git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: xcode version
         run: xcodebuild -version -sdk