Bump actions/checkout from 2.3.5 to 2.4.0

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] <support@github.com>

Author: dependabot[bot]

.github/workflows/main.yaml

@@ -12,7 +12,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - uses: actions/setup-python@v2.2.2
       - uses: pre-commit/action@v2.0.3
 
@@ -23,7 +23,7 @@ jobs:
       matrix:
         python-version: [3.7, 3.8, 3.9]
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - name: Setup Python
         uses: actions/setup-python@v2.2.2
         with:
@@ -50,7 +50,7 @@ jobs:
       matrix:
         python-version: [3.8, 3.9]
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - name: Setup Python
         uses: actions/setup-python@v2.2.2
         with: