Fix setup-rust-toolchain with.target

The old `dtolnay` action used `targets` here, and there is no up-front
validation of the schema, so this was easy to miss when making the
previous change.

Author: chriskrycho

.github/workflows/release.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Set up cargo
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          targets: aarch64-apple-darwin,x86_64-apple-darwin
+          target: aarch64-apple-darwin,x86_64-apple-darwin
       - name: Cargo Cache
         uses: Swatinem/rust-cache@v2
       - name: Compile and package Volta