Bump actions/checkout from 2.3.4 to 2.4.0 (exercism#1024)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.3.4 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@5a4ac90...ec3a7ce)

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

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

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

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:
-      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
+      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
 
       - uses: actions/setup-go@bfdd3570ce990073878bf10f6b2d79082de49492
         with:
@@ -37,7 +37,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
+      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
 
       - name: Check formatting
         run: ./.gha.gofmt.sh

.github/workflows/sync-labels.yml

@@ -15,7 +15,7 @@ jobs:
     name: Sync labels
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
+      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
       - uses: micnncim/action-label-syncer@3abd5ab72fda571e69fffd97bd4e0033dd5f495c
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}