Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/autofix.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Validate Gradle wrappers
         uses: gradle/actions/wrapper-validation@v4
   autofix:
@@ -21,7 +21,7 @@ jobs:
       - validation
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup Java
         uses: actions/setup-java@v4

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Validate Gradle wrappers
         uses: gradle/actions/wrapper-validation@v4
   assemble:
@@ -18,7 +18,7 @@ jobs:
 
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Setup Java
         uses: actions/setup-java@v4
         with:
@@ -34,7 +34,7 @@ jobs:
 
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Setup Java
         uses: actions/setup-java@v4
         with:
@@ -50,7 +50,7 @@ jobs:
 
     steps:
       - name: Checkout Git repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Setup Java
         uses: actions/setup-java@v4
         with:

.github/workflows/classroom.yml

@@ -12,7 +12,7 @@ jobs:
     if: github.actor != 'github-classroom[bot]'
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Works with an empty array
       id: works-with-an-empty-array
       uses: classroom-resources/autograding-command-grader@v1