Update GitHub Actions actions/checkout@v2 to v3

The v2 implementation uses Node 12, which is end-of-life on April 30, 2022.
See https://nodejs.org/en/about/releases/. Update to v3, which is based on
Node 16 whose support lasts until April 30, 2024.

Author: dtolnay

.github/workflows/clippy.yml

@@ -37,7 +37,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Install toolchain
       run: rustup show active-toolchain

.github/workflows/clippy_bors.yml

@@ -25,7 +25,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
       with:
         ref: ${{ github.ref }}
 
@@ -88,7 +88,7 @@ jobs:
       if: matrix.host == 'i686-unknown-linux-gnu'
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Install toolchain
       run: rustup show active-toolchain
@@ -154,7 +154,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Install toolchain
       run: rustup show active-toolchain
@@ -212,7 +212,7 @@ jobs:
         github_token: "${{ secrets.github_token }}"
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Install toolchain
       run: rustup show active-toolchain

.github/workflows/clippy_dev.yml

@@ -23,7 +23,7 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     # Run
     - name: Build

.github/workflows/deploy.yml

@@ -21,10 +21,10 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
       with:
         ref: ${{ env.TARGET_BRANCH }}
         path: 'out'

.github/workflows/remark.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
     # Setup
     - name: Checkout
-      uses: actions/checkout@v2.3.3
+      uses: actions/checkout@v3.0.2
 
     - name: Setup Node.js
       uses: actions/setup-node@v1.4.4