.github: Bump actions/checkout from 2 to 3 (#25)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

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

Signed-off-by: dependabot[bot] <[email protected]>

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

.github/workflows/build.yml

@@ -47,7 +47,7 @@ jobs:
       with:
         go-version: 1.15
     - name: Check out code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Install Git
       run: misc/build-git.bash ~/git ${{ matrix.git }}
     - name: Download dependencies
@@ -75,7 +75,7 @@ jobs:
       with:
         go-version: 1.15
     - name: Check out code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Install Git
       run: misc/build-git.bash ~/git 2.27.0
     - name: Download dependencies
@@ -101,7 +101,7 @@ jobs:
       with:
         go-version: 1.15
     - name: Check out code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Download dependencies
       run: go mod download
       env: