Try to workaround docker/buildx#395

Dockerfile

@@ -13,7 +13,10 @@ RUN USER=rust cargo new /home/rust/tokio_modbus-winets
 RUN USER=rust cargo new /home/rust/modbus-mqtt
 WORKDIR /home/rust/modbus-mqtt
 ADD --chown=rust:rust Cargo.lock modbus-mqtt/Cargo.toml ./
-RUN cargo build --release
+RUN mkdir -p /home/rust/modbus-mqtt/target/release
+RUN --mount=type=cache,target=/home/rust/modbus-mqtt/target,sharing=locked \
+    --mount-type=cache,target=/usr/local/cargo/registry,sharing=locked \
+    cargo build --release
 
 # # Delete files & directories which shouldn't exist for the workspace
 # RUN rm -rf src
@@ -22,7 +25,9 @@ RUN cargo build --release
 ADD --chown=rust:rust . ./
 
 # Build our application.
-RUN cargo build --release
+RUN --mount=type=cache,target=/home/rust/modbus-mqtt/target,sharing=locked \
+    --mount-type=cache,target=/usr/local/cargo/registry,sharing=locked \
+    cargo build --release --offline && mv target/release/modbus-mqtt ./bin
 
 # Now, we need to build our _real_ Docker container, copying in `bump-api`.
 FROM debian:bullseye-slim
@@ -34,8 +39,8 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     libudev1
 
 COPY --from=builder \
-    /home/rust/modbus-mqtt/target/release/modbus-mqtt \
-    /usr/local/bin/
+    /home/rust/modbus-mqtt/bin \
+    /usr/local/bin/modbus-mqtt
 
 ENV RUST_LOG=warn,modbus_mqtt=info