Bump actions/checkout from 2.3.5 to 2.4.0 (#1058)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.3.5 to 2.4.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2.3.5...v2.4.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
           - {VERSION: "3.9", TOXENV: "docs"}
     name: "${{ matrix.PYTHON.TOXENV }}"
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - name: Setup python
         uses: actions/[email protected]
         with:
@@ -66,7 +66,7 @@ jobs:
           - {CONTAINER: "ubuntu-rolling", TOXENV: "py39-cryptographyMain"}
     name: "${{ matrix.TEST.TOXENV }} on ${{ matrix.TEST.CONTAINER }}"
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - run: tox -v
         env:
           TOXENV: ${{ matrix.TEST.TOXENV }}