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](actions/checkout@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>

Author: dependabot[bot]

.github/workflows/additional.yml

@@ -11,7 +11,7 @@ jobs:
     env:
       COLUMNS: 120
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: astral-sh/setup-uv@v7
       - run: |
           uv run --with 'minimum-dependency-versions @ git+https://github.com/xarray-contrib/minimum-dependency-versions@v1.0.0' \
@@ -25,7 +25,7 @@ jobs:
     runs-on: "ubuntu-latest"
 
     steps:
-      - uses: actions/checkout@v5
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
+      - uses: actions/checkout@v6
       - uses: prefix-dev/setup-pixi@v0.9.0
       - run: pixi run docs-linkcheck

.github/workflows/cache-pixi-lock.yml

@@ -17,7 +17,7 @@ jobs:
     outputs:
       cache-id: ${{ steps.restore.outputs.cache-primary-key }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           submodules: recursive

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
           - os: ubuntu
             pixi-environment: "test-minimum"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Restore cached pixi lockfile
         uses: actions/cache/restore@v4
         id: restore-pixi-lock
@@ -101,7 +101,7 @@ jobs:
           - os: ubuntu
             python-version: "3.11"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Restore cached pixi lockfile
         uses: actions/cache/restore@v4
         id: restore-pixi-lock
@@ -149,7 +149,7 @@ jobs:
     needs: [cache-pixi-lock]
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Restore cached pixi lockfile
         uses: actions/cache/restore@v4
         id: restore-pixi-lock

.github/workflows/nightly.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Build conda package
         uses: prefix-dev/rattler-build-action@v0.2.34
         with:

.github/workflows/pypi-release.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'Parcels-code/parcels'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-python@v6