docker: speed up docker image build (ethereum#24796)

This PR improves the docker build speed for repeated builds where go.mod and go.sum do no change, by placing the downloaded dependencies in a lower layer

Author: eval-exec

Dockerfile

@@ -7,6 +7,10 @@ ARG BUILDNUM=""
 FROM golang:1.17-alpine as builder
 
 RUN apk add --no-cache make gcc musl-dev linux-headers git bash
+# Get dependencies - will also be cached if we won't change go.mod/go.sum
+COPY go.mod /go-ethereum/
+COPY go.sum /go-ethereum/
+RUN cd /go-ethereum && go mod download
 
 ADD . /go-ethereum
 RUN cd /go-ethereum && go run build/ci.go install ./cmd/geth

Dockerfile.alltools

@@ -7,6 +7,10 @@ ARG BUILDNUM=""
 FROM golang:1.17-alpine as builder
 
 RUN apk add --no-cache gcc musl-dev linux-headers git
+# Get dependencies - will also be cached if we won't change go.mod/go.sum
+COPY go.mod /go-ethereum/
+COPY go.sum /go-ethereum/
+RUN cd /go-ethereum && go mod download
 
 ADD . /go-ethereum
 RUN cd /go-ethereum && go run build/ci.go install