Update dendrite/Dockerfile, dendrite/Makefile files

dendrite/Dockerfile

@@ -1,9 +1,10 @@
 FROM golang:buster as builder
 
 ARG DEBIAN_FRONTEND=noninteractive
-COPY dendrite /dendrite
-WORKDIR /dendrite
-RUN rm -rf .git && ./build.sh
+ARG VERSION
+WORKDIR /
+RUN git clone -b v${VERSION} --depth 1 https://github.com/matrix-org/dendrite.git && \
+    cd dendrite && rm -rf .git && ./build.sh
 
 FROM debian:buster-20210111-slim
 

dendrite/Makefile

@@ -3,13 +3,13 @@ include version
 
 IMAGE=dendrite
 
-nopush: git-clone
+nopush:
 	docker buildx build --platform linux/amd64 --load \
 	    --build-arg VERSION=$(VERSION) \
     	    --tag ${NAMESPACE}/${IMAGE}:$(VERSION) \
 	    --tag ${CI_REGISTRY_IMAGE}/${IMAGE}:$(VERSION) .
 
-push: git-clone
+push:
 	docker buildx build --platform linux/amd64,linux/arm64 --push \
 	    --build-arg VERSION=$(VERSION) \
     	    --cache-from=type=registry,ref=${NAMESPACE}/buildx:${IMAGE} \