fix: ensure stable toolchain is specified in Rust setup

Author: davidonet

.github/workflows/build.yml

@@ -59,6 +59,7 @@ jobs:
 
       - uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: stable
           targets: ${{ matrix.target }}
 
       - uses: swatinem/rust-cache@v2