Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/publish.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     environment: release
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-java@v5

.github/workflows/tests.yaml

@@ -13,7 +13,7 @@ jobs:
   check-pre-commit:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.13"
@@ -22,7 +22,7 @@ jobs:
   test-coverage:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v5
         with:
           java-version: 17
@@ -42,7 +42,7 @@ jobs:
         java: [17, 21]
         spring-boot: [3.0.13, 3.1.12, 3.2.12, 3.3.8, 3.4.3]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v5
         with:
           java-version: ${{ matrix.java }}