Update actions/checkout from v4 to v5 (#24)

Author: OskarStark

.github/workflows/pipeline.yml

@@ -14,7 +14,7 @@ jobs:
         dependencies: ['lowest', 'highest']
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -40,7 +40,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2