Update actions/checkout in GitHub Actions workflows to v4

Author: striezel

.github/workflows/main.yml

@@ -13,7 +13,7 @@ jobs:
   lints:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
@@ -31,7 +31,7 @@ jobs:
         os: ['ubuntu-latest', 'windows-latest', 'macos-latest']
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - uses: actions-rs/cargo@v1
     - uses: actions-rs/toolchain@v1
       with:
@@ -41,7 +41,7 @@ jobs:
   wasm:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - uses: actions-rs/toolchain@v1
       with:
        toolchain: stable
@@ -52,7 +52,7 @@ jobs:
   #   needs: test
   #   steps:
   #     - name: Checkout
-  #       uses: actions/checkout@v2.3.1
+  #       uses: actions/checkout@v4
   #     - name: Build the book
   #       run: cd guide && mdbook build
   #     - name: Deploy
@@ -61,4 +61,4 @@ jobs:
   #       with:
   #         branch: master
   #         folder: guide/book
-  #         token: ${{ secrets.GITHUB_TOKEN }}
+  #         token: ${{ secrets.GITHUB_TOKEN }}