chore: skip Go proxy for lambda-go integ tests (#14727)

Privacy-conscious users and/or organizations may choose to skip sending all
package requests to the Google proxy (as is default). Some corporate
environments may block network access to proxy.golang.org altogether.

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packages/@aws-cdk/aws-lambda-go/lib/Dockerfile

@@ -5,6 +5,7 @@ FROM $IMAGE
 
 # set the GOCACHE
 ENV GOCACHE=$GOPATH/.cache/go-build
+ENV GOPROXY=direct
 
 # Ensure all users can write to GOPATH
 RUN chmod -R 777 $GOPATH