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>

Author: dependabot[bot]

.github/workflows/pythonpackage.yml

@@ -21,7 +21,7 @@ jobs:
         python-version: [3.7, 3.7.5, 3.7.12, 3.8, 3.8.0, 3.8.11, 3.8, 3.9, 3.9.0, 3.9.7, "3.10"]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 9999
     - name: Set up Python ${{ matrix.python-version }}