Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/assets.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: recursive
       - name: Install pnpm
@@ -39,7 +39,7 @@ jobs:
       - name: Install pnpm dependencies
         run: pnpm install
       - name: Checkout ab (optional)
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: lichess-org/ab
           ssh-key: ${{ secrets.id_rsa_ab }}

.github/workflows/flair.yml

@@ -14,6 +14,6 @@ jobs:
   validate-flair:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: sudo apt-get update && sudo apt-get install -y imagemagick
       - run: ./bin/validate-flair public/flair/img/

.github/workflows/lint.yml

@@ -23,7 +23,7 @@ jobs:
           - lint
           - check-format
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v6
         with:
@@ -35,7 +35,7 @@ jobs:
   codeql:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: github/codeql-action/init@v4
         with:
           languages: javascript

.github/workflows/server.yml

@@ -37,7 +37,7 @@ jobs:
       matrix:
         java-version: [21, 25]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v5
         with:
           distribution: temurin
@@ -61,7 +61,7 @@ jobs:
   format:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-java@v5
         with:
           distribution: temurin

.github/workflows/translations.yml

@@ -16,7 +16,7 @@ jobs:
   translations:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install xmllint
         run: sudo apt-get update && sudo apt-get install -y libxml2-utils
       - name: Validate translation files