Fix Dockerfile go dependency caching (#2626)

The current Dockerfile uses a bind mount when downloading the go dependencies.
This causes the entire project folder to be added to the Docker context when
only the `go.mod` and `go.sum` files are needed.  This ends up breaking the
caching of the dependencies as any change to any file in the project will cause
the docker context to change.  Removing this bind mount allows the dependencies
to be correctly cached.

Author: hintofbasil

Dockerfile

@@ -8,7 +8,6 @@ COPY go.sum go.sum
 # cache deps before building and copying source so that we don't need to re-download as much
 # and so that source changes don't invalidate our downloaded layer
 RUN --mount=type=bind,target=. \
-    --mount=type=cache,target=/root/.cache/go-build \
     GOPROXY=direct go mod download
 
 FROM base AS build