Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/release.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup cache
         uses: actions/cache@v4

.github/workflows/test.yml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/cache@v4
         with:
           path: ~/.m2/repository