build(deps): bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

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

.github/workflows/lint.yml

@@ -5,7 +5,7 @@ jobs:
     name: cargo fmt
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: rustup show && rustup update
       - name: cargo fmt
@@ -15,7 +15,7 @@ jobs:
     name: cargo clippy
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: rustup show && rustup update
       - name: cargo clippy
@@ -25,7 +25,7 @@ jobs:
     name: cargo readme
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo +stable install cargo-readme
       - run: cd ciborium-io && cargo readme > README.md

.github/workflows/test.yml

@@ -5,7 +5,7 @@ jobs:
     name: test ${{ matrix.toolchain }} ${{ matrix.profile.name }} ${{ matrix.crates.name }} ${{ matrix.crates.feat }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup toolchain install ${{ matrix.toolchain }}
       - name: cargo test