chore(deps): update actions/checkout action to v6 (#28)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -55,7 +55,7 @@ jobs:
           - { platform: watchOS, name: "watchOS 10.4", xcode: "Xcode_15.3", runsOn: macOS-14, destination: "OS=10.4,name=Apple Watch Series 9 (45mm)" }
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6
       - name: Run tests - ${{ matrix.name }}
         run: |
           xcodebuild test \
@@ -87,7 +87,7 @@ jobs:
           - { name: "macOS 14, SPM 5.10.0", xcode: "Xcode_15.3", runsOn: macOS-14 }
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6
       - name: Build with Swift Package Manager - ${{ matrix.name }}
         run: swift build -c release