toolchain in recipe.json is ignored in `cargo chef cook`

cargo chef cook generates rust-toolchain.toml file, but it's not used in the subsequent build of dependencies.
rust-toolchain.toml takes effect when cargo is invoked next time. Therefore, executing cargo chef cook twice results in building with the wrong toolchain for the first time and the correct building for the second time.

The following Dockerfile reproduces the problem.

FROM lukemathwalker/cargo-chef:latest-rust-1 AS chef
WORKDIR /app

FROM chef AS planner
RUN echo '[workspace]\nresolver = "2"\nmembers = ["hello"]' > Cargo.toml
RUN cargo new hello
RUN echo '[toolchain]\nchannel = "1.75.0"' > rust-toolchain.toml
RUN cargo chef prepare --recipe-path recipe.json

FROM chef AS builder
COPY --from=planner /app/recipe.json recipe.json
RUN cargo chef cook --release --recipe-path recipe.json # does not install 1.75.0
RUN cargo chef cook --release --recipe-path recipe.json # does install 1.75.0

Start with the Dockerfile reproduction and inspect how cargo chef cook processes recipe.json and the generated rust-toolchain.toml. Verify the first cook invocation uses the toolchain declared in the recipe, then rerun the two cook commands to confirm the second-run discrepancy is gone.