Update actions/checkout action to v6 (#489)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/broken-links.yml

@@ -10,7 +10,7 @@ jobs:
     name: Check for broken links in README.md
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up Node
         uses: actions/setup-node@v6

.github/workflows/maven.yml

@@ -10,7 +10,7 @@ jobs:
     name: Build Application
     steps:
       - name: Checkout Code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup for JDK 21
         uses: actions/setup-java@v5

.github/workflows/verify-local-development.yml

@@ -15,7 +15,7 @@ jobs:
     name: Verify spring-boot:run startup
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up JDK 21
         uses: actions/setup-java@v5
@@ -43,7 +43,7 @@ jobs:
     name: Verify spring-boot:test-run startup
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up JDK 21
         uses: actions/setup-java@v5