Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...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/audits.yml

@@ -10,7 +10,7 @@ jobs:
     name: Vet Rust dependencies
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
         id: toolchain
       - run: rustup override set ${{steps.toolchain.outputs.name}}

.github/workflows/book.yml

@@ -13,7 +13,7 @@ jobs:
 
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Setup mdBook
         uses: peaceiris/actions-mdbook@v1

.github/workflows/checks.yml

@@ -13,12 +13,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the base branch
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
       - name: Check out the PR branch
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: ${{ github.head_ref }}
           fetch-depth: 0

.github/workflows/lints.yml

@@ -8,7 +8,7 @@ jobs:
     name: Scripted diffs
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
           ref: ${{ github.event.pull_request.head.sha }}
@@ -19,7 +19,7 @@ jobs:
     name: General
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: sudo python3 -m pip install yq
 
@@ -62,7 +62,7 @@ jobs:
     name: Python
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: sudo python3 -m pip install pyflakes
 
@@ -78,7 +78,7 @@ jobs:
     name: Clippy (MSRV)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run clippy
         uses: actions-rs/clippy-check@v1
         with:
@@ -90,5 +90,5 @@ jobs:
     name: Rustfmt
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - run: cargo fmt -- --check