Fix CI: Remove redundant toolchain input from dtolnay/rust-toolchain@stable

The dtolnay/rust-toolchain action already specifies the toolchain version
in the action reference (@stable). Adding toolchain: stable as an input
was causing 'toolchain is a required input' errors.

Fixed in:
- ci.yml
- release.yml
- crates-publish.yml

.github/workflows/release.yml

@@ -30,7 +30,6 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
         with:
-          toolchain: stable
           targets: ${{ matrix.target }}
       - run: cargo build --release --target ${{ matrix.target }}
       - name: Rename binary