Update actions/checkout action to v6 (eikek#541)

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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
       matrix:
         java: [ 'openjdk@1.11' ]
     steps:
-      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+      - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
         with:
           fetch-depth: 100
       - name: Fetch tags

.github/workflows/release.yml

@@ -8,7 +8,7 @@ jobs:
   release:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+      - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
         with:
           fetch-depth: 0
       - uses: olafurpg/setup-scala@v14