Bump actions/checkout from 2 to 2.3.4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 2.3.4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v2...v2.3.4)

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

Closes #4

Change-Id: Ic2fe2568d1680ec37efebb82344c15f3dcc2a2b7
diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
index 5a42f99..21d864e 100644
--- a/.github/workflows/pythonpackage.yml
+++ b/.github/workflows/pythonpackage.yml
@@ -26,7 +26,7 @@
             r-version: 3.6
             python-version: 3.9
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v2
       with: