Update to actions/checkout@v4 (#26)

Author: lambda-fairy

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
     steps:
 
     - name: Check out repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Install Rust
       uses: actions-rs/toolchain@v1