ci: bump actions/checkout

Author: wezm

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     continue-on-error: ${{ matrix.experimental }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@v1
         with:
           toolchain: ${{ matrix.rust }}