Bump actions/checkout from 5 to 6 (#20)

https://github.com/actions/checkout/releases

Author: spaze

.github/workflows/php.yml

@@ -21,7 +21,7 @@ jobs:
             - "--prefer-lowest"
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: OS info
       run: cat /etc/os-release