Fix Dockerfile

Dockerfile

@@ -1,18 +1,37 @@
-from ruby:2.7.2-slim
+from ruby:3.0.0-slim
 
 RUN apt update && apt -y upgrade
-RUN apt install -y bison make git gcc gcc-arm-linux-gnueabi qemu qemu-kvm qemu-system-arm
+RUN apt install -y \
+  bison \
+  gcc \
+  gcc-arm-linux-gnueabi \
+  git \
+  make \
+  qemu \
+  qemu-kvm \
+  qemu-system-arm
 
 RUN gem update --system
 
-RUN git clone https://github.com/mruby/mruby /root/mruby
-ARG MRUBY_TAG
-RUN cd /root/mruby; git checkout $MRUBY_TAG; make
+ARG USER_ID
+RUN useradd -m -u $USER_ID mrubyc
+RUN mkdir /work && chown mrubyc /work
+
+USER mrubyc
 
-VOLUME /root/mrubyc
-COPY Gemfile /root/mrubyc/
-COPY Gemfile.lock /root/mrubyc/
-WORKDIR /root/mrubyc
+VOLUME /work/mrubyc
+COPY --chown=mrubyc Gemfile /work/mrubyc/
+COPY --chown=mrubyc Gemfile.lock /work/mrubyc/
+
+USER root
+WORKDIR /work/mrubyc
 RUN bundle install
+
+USER mrubyc
 ENV CFLAGS="-DMRBC_USE_MATH=1 -DMAX_SYMBOLS_COUNT=500"
-CMD ["bundle", "exec", "mrubyc-test", "-e", "100", "-p", "/root/mruby/build/host/bin/mrbc"]
+
+RUN git clone https://github.com/mruby/mruby /work/mruby
+ARG MRUBY_TAG
+RUN cd /work/mruby; git fetch --prune; git checkout $MRUBY_TAG; make clean && make
+
+CMD ["bundle", "exec", "mrubyc-test", "-e", "10", "-p", "/work/mruby/build/host/bin/mrbc"]