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] <[email protected]>

.github/workflows/autograding.yml

@@ -10,7 +10,7 @@ jobs:
   Build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - name: Set up JDK 11
         uses: actions/setup-java@v2
         with:

.github/workflows/check-md-links.yml

@@ -6,7 +6,7 @@ jobs:
   markdown-link-check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - uses: gaurav-nelson/[email protected]
         with:
           check-modified-files-only: 'yes'

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
     name: on ${{ matrix.platform }}
 
     steps:
-    - uses: actions/checkout@v2.3.5
+    - uses: actions/checkout@v2.4.0
     - name: Set up JDK 11
       uses: actions/setup-java@v2
       with:

.github/workflows/coverage.yml

@@ -13,7 +13,7 @@ jobs:
     name: Coverage on Ubuntu
 
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - name: Set up JDK 11
         uses: actions/setup-java@v2
         with:

.github/workflows/sync-labels.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2.3.5
+      - uses: actions/checkout@v2.4.0
       - uses: micnncim/[email protected]
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}