gh actions: switch actions/checkout version to main

Author: floooh

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
         os: [ubuntu-latest, windows-latest]
     runs-on: ${{matrix.os}}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@main
       - name: setup-rust
         uses: dtolnay/rust-toolchain@master
         with: