Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/kivy_ios.yml

@@ -28,7 +28,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout kivy-ios
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Set up Python 3.x
       uses: actions/setup-python@v6
       with: