Fix Docker build by using --locked for cargo-chef install (#2222)

cargo-chef's transitive dependencies (cargo-platform, cargo_metadata,
guppy, target-spec) bumped their MSRV to Rust 1.86-1.88, breaking the
install on our pinned Rust 1.85.0 toolchain. Using --locked forces cargo
to use cargo-chef's bundled lockfile, which is tested against its
supported Rust versions.

Author: penberg

Dockerfile

@@ -15,7 +15,7 @@ RUN cat rust-toolchain.toml | grep "channel" | awk '{print $3}' | sed 's/\"//g'
     && rustup update $(cat toolchain.txt) \
     && rustup default $(cat toolchain.txt) \
     && rm toolchain.txt rust-toolchain.toml \
-    && cargo install cargo-chef
+    && cargo install cargo-chef --locked
 
 FROM chef AS planner
 ARG BUILD_DEBUG=false