Mark the init script as executable and make the fake agent use the same arg format

Author: Stuart133

runner-init/fake-agent.Dockerfile

@@ -1,14 +1,8 @@
 FROM busybox:stable-musl as build
 
-FROM scratch as temp
-
 ARG ARCH=amd64
 
 COPY ./bin/circleci-fake-agent-${ARCH} /opt/circleci/circleci-agent
-COPY --from=build /bin/cp /bin/cp
-
-FROM scratch
-
-COPY --from=temp / /
+COPY ./runner-init/init.sh /init.sh
 
-ENTRYPOINT ["/bin/cp"]
+ENTRYPOINT ["/init.sh"]