ci: Update to `actions/checkout@v4` from `v3`.

This also updates the book's section on CI for the same thing.

changelog: none

.github/workflows/clippy.yml

@@ -38,7 +38,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install toolchain
       run: rustup show active-toolchain

.github/workflows/clippy_bors.yml

@@ -26,7 +26,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         ref: ${{ github.ref }}
 
@@ -72,7 +72,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install i686 dependencies
       if: matrix.host == 'i686-unknown-linux-gnu'
@@ -151,7 +151,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install toolchain
       run: rustup show active-toolchain
@@ -175,7 +175,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install toolchain
       run: rustup show active-toolchain
@@ -231,7 +231,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install toolchain
       run: rustup show active-toolchain

.github/workflows/clippy_dev.yml

@@ -24,7 +24,7 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     # Run
     - name: Build

.github/workflows/deploy.yml

@@ -21,10 +21,10 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         ref: ${{ env.TARGET_BRANCH }}
         path: 'out'

.github/workflows/remark.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Setup Node.js
       uses: actions/setup-node@v3

book/src/continuous_integration/github_actions.md

@@ -15,7 +15,7 @@ jobs:
   clippy_check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run Clippy
         run: cargo clippy --all-targets --all-features
 ```