Update actions/checkout to v6

Author: JanTvrdik

.github/workflows/checks.yml

@@ -17,7 +17,7 @@ jobs:
         steps:
             -
                 name: Checkout code
-                uses: actions/checkout@v4
+                uses: actions/checkout@v6
             -
                 name: Setup PHP
                 uses: shivammathur/setup-php@v2

.github/workflows/lint.yml

@@ -13,7 +13,7 @@ jobs:
         steps:
             -
                 name: Checkout code
-                uses: actions/checkout@v4
+                uses: actions/checkout@v6
 
             -
                 name: Install dependencies