Detect arch in a script and target linux-musl

hole-punching-tests/Dockerfile

@@ -1,15 +1,21 @@
 # syntax=docker/dockerfile:1.5-labs
 FROM rust:1.72.0 as builder
 
+ARG RUST_TARGET
+
+RUN rustup target add $RUST_TARGET
+
 RUN --mount=type=cache,target=/var/cache/apt apt-get update && apt-get install -y musl-dev musl-tools
 
 # Run with access to the target cache to speed up builds
 WORKDIR /workspace
 ADD . .
 RUN --mount=type=cache,target=./target \
     --mount=type=cache,target=/usr/local/cargo/registry \
-    cargo build --release --package hole-punching-tests && \
-    mv ./target/release/hole-punching-tests /usr/local/bin/hole-punching-tests
+    cargo build --release --package hole-punching-tests --target $RUST_TARGET
+
+RUN --mount=type=cache,target=./target \
+    mv ./target/$RUST_TARGET/release/hole-punching-tests /usr/local/bin/hole-punching-tests
 
 FROM alpine:3
 COPY --from=builder /usr/local/bin/hole-punching-tests /usr/bin/hole-punch-client