Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/SwiftyESBuild.yml

@@ -28,7 +28,7 @@ jobs:
           - '5'
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Use a cache for ".build" directory.
       uses: actions/cache@v4
       with: