Bump actions/checkout from 5 to 6 (#352)

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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci-additional.yml

@@ -23,7 +23,7 @@ jobs:
 
     steps:
       - name: checkout the repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # need to fetch all tags to get a correct version
           fetch-depth: 0 # fetch all branches and tags

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     outputs:
       triggered: ${{ steps.detect-trigger.outputs.trigger-found }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 2
       - uses: xarray-contrib/ci-trigger@v1
@@ -55,7 +55,7 @@ jobs:
 
     steps:
       - name: checkout the repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # need to fetch all tags to get a correct version
           fetch-depth: 0 # fetch all branches and tags

.github/workflows/nightly.yml

@@ -24,7 +24,7 @@ jobs:
     outputs:
       triggered: ${{ steps.detect-trigger.outputs.trigger-found }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 2
       - uses: xarray-contrib/[email protected]
@@ -57,7 +57,7 @@ jobs:
 
     steps:
       - name: checkout the repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # need to fetch all tags to get a correct version
           fetch-depth: 0 # fetch all branches and tags

.github/workflows/pypi.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'xarray-contrib/pint-xarray'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0