ci: Add cleanup

Author: hdiethelm

.github/docker/Dockerfile

@@ -13,6 +13,11 @@ RUN  cd linuxcnc-src && \
      debian/configure && \
      apt-get build-dep -y .
 
+#Cleanup
+RUN apt-get clean && \
+    rm -rf /var/lib/apt/lists/* && \
+    rm -rf linuxcnc-src
+
 #Add a user for linuxcnc with sudo nopasswd and set it as user
 RUN useradd -ms /bin/bash linuxcnc && \
     echo "linuxcnc ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers.d/linuxcnc-nopasswd