Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
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/ci.yml

@@ -14,7 +14,7 @@ jobs:
         name: Flake8
         runs-on: ubuntu-latest
         steps:
-        -   uses: actions/checkout@v3
+        -   uses: actions/checkout@v4
         -
             uses: actions/setup-python@v4
             with:
@@ -31,7 +31,7 @@ jobs:
             matrix:
                 python-version: ['3.8', '3.9', '3.x']
         steps:
-        -   uses: actions/checkout@v3
+        -   uses: actions/checkout@v4
         -
             uses: actions/setup-python@v4
             with: