Bump actions/checkout from 2 to 4 (#142)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Lukas Pilz <lukas.pilz@iup.uni-heidelberg.de>

.github/workflows/ci.yaml

@@ -25,7 +25,7 @@ jobs:
       matrix:
         python-version: ['3.8', '3.9', '3.10']
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: set up conda environment
         uses: mamba-org/setup-micromamba@v1
         with:

.github/workflows/pypi-release.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'xarray-contrib/xwrf'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - uses: actions/setup-python@v4

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

@@ -24,7 +24,7 @@ jobs:
       matrix:
         python-version: ['3.10']
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: set up conda environment
         id: conda
         uses: mamba-org/setup-micromamba@v1