Make the build use less space on the CI host

High space usage could cause the docker layer cache to fail while packaging the layers.

.github/workflows/ci-workflow.yml

@@ -57,3 +57,6 @@ jobs:
         with:
           name: artifacts
           path: target/
+      # Make room for the docker layer caching to package up layers
+      - name: Cleanup
+        run: rm -fr *

Dockerfile

@@ -22,10 +22,11 @@ RUN curl https://downloads.apache.org/maven/maven-3/3.6.3/binaries/apache-maven-
 ENV PATH=/home/build/apache-maven-3.6.3/bin:$PATH
 
 # Prepare a snapshot of Netty 5
-RUN git clone -b master https://github.com/netty/netty.git netty
-WORKDIR /home/build/netty
-RUN mvn install -DskipTests -T1C -B -am
-WORKDIR /home/build
+RUN git clone --depth 1 -b master https://github.com/netty/netty.git netty \
+    && cd netty \
+    && mvn install -DskipTests -T1C -B -am \
+    && cd .. \
+    && rm -fr netty
 
 # Prepare our own build
 COPY pom.xml pom.xml

Makefile

@@ -1,4 +1,4 @@
-.PHONY: image test dbg clean build
+.PHONY: image test dbg clean build rebuild
 .DEFAULT_GOAL := build
 
 image: