Bump actions/checkout from 5 to 6 (#234)

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.yaml

@@ -25,7 +25,7 @@ jobs:
       matrix:
         python-version: ["3.11", "3.12", "3.13"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: set up conda environment
         uses: mamba-org/setup-micromamba@v2
         with:

.github/workflows/pypi-release.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'xarray-contrib/xwrf'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-python@v6

.github/workflows/upstream-dev-ci.yaml

@@ -24,7 +24,7 @@ jobs:
       matrix:
         python-version: ["3.13"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: set up conda environment
         id: conda
         uses: mamba-org/setup-micromamba@v2