Bump actions/checkout from 2 to 3

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

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

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

.github/workflows/release_and_publish.yml

@@ -26,7 +26,7 @@
      runs-on: ubuntu-latest
      steps:
        - name: Checkout repo
-         uses: actions/checkout@v2
+         uses: actions/checkout@v3
 
        - name: Set up python
          uses: actions/setup-python@v2

.github/workflows/unittests.yml

@@ -24,7 +24,7 @@
        run:
          shell: bash -l {0}
      steps:
-       - uses: actions/checkout@v2
+       - uses: actions/checkout@v3
        - uses: conda-incubator/setup-miniconda@v2
          with:
            environment-file: ${{ matrix.environment-file }}