Bump actions/checkout from 2 to 3

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]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Install Rust
       uses: actions-rs/toolchain@v1
       with:

.github/workflows/fmt.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Run rustfmt check
         run: |
           rustup component add rustfmt