Update actions/checkout requirement to v2.3.4

Updates the requirements on [actions/checkout](https://github.com/actions/checkout) to permit the latest version.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/commits/5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f)

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

Author: dependabot[bot]

.github/workflows/release.yml

@@ -7,7 +7,7 @@ jobs:
 
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2.3.4
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v1
       with:

.github/workflows/tests.yml

@@ -15,7 +15,7 @@ jobs:
         run: sudo apt-get install gettext -y
       - uses: actions/setup-python@v2
       - run: python -m pip install --upgrade pip setuptools wheel twine readme-renderer
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
       - run: python setup.py sdist bdist_wheel
       - run: python -m twine check dist/*
 
@@ -35,7 +35,7 @@ jobs:
       uses: actions/setup-python@v1
       with:
         python-version: ${{ matrix.python-version }}
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2.3.4
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip setuptools codecov