security: bump actions/checkout from 2 to 2.4.0 (Azure#764)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 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...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/cover.yaml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       # pinning to the sha 5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f from https://github.com/actions/checkout/releases/tag/v2.3.4
-      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
+      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
       # pinning to the sha 331ce1d993939866bb63c32c6cbbfd48fa76fc57 from https://github.com/actions/setup-go/releases/tag/v2.1.4
       - uses: actions/setup-go@331ce1d993939866bb63c32c6cbbfd48fa76fc57
         with:

.github/workflows/gh-pages.yaml

@@ -9,7 +9,7 @@ jobs:
   deploy:
     runs-on: ubuntu-18.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
         with:
           submodules: true # Fetch Hugo themes (true OR recursive)
           fetch-depth: 0 # Fetch all history for .GitInfo and .Lastmod