Update actions/checkout action to v4

Author: taiki-e

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
         os: [ubuntu-latest]
         rust: [nightly, beta, stable]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
       - run: rustup target add thumbv7m-none-eabi
@@ -59,7 +59,7 @@ jobs:
         # Rust version in Cargo.toml.
         rust: ['1.59']
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
       - run: cargo build
@@ -72,23 +72,23 @@ jobs:
   clippy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup update stable
       - run: cargo clippy --all-features --all-targets
 
   fmt:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup update stable
       - run: cargo fmt --all --check
 
   miri:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install Rust
         run: rustup toolchain install nightly --component miri && rustup default nightly
       - run: cargo miri test
@@ -103,7 +103,7 @@ jobs:
       issues: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       # https://github.com/rustsec/audit-check/issues/2
       - uses: rustsec/audit-check@master
         with:

.github/workflows/release.yml

@@ -13,7 +13,7 @@ jobs:
     if: github.repository_owner == 'smol-rs'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: taiki-e/create-gh-release-action@v1
         with:
           changelog: CHANGELOG.md