gomega executing network calls in unit tests

[jessicayuen]

Unable to run these unit tests in a jailed/network-less environment:

14:26:06  FAIL	github.com/envoyproxy/xds-relay/internal/app/cache [setup failed]
14:26:06  # github.com/envoyproxy/xds-relay/internal/app/mapper
14:26:06  package github.com/envoyproxy/xds-relay/internal/app/mapper (test)
14:26:06  	imports github.com/onsi/ginkgo: github.com/onsi/ginkgo@v1.12.0: Get "<url>/github.com/onsi/ginkgo/@v/v1.12.0.zip": dial tcp: lookup <url> on <ip>: dial udp <ip>: connect: network is unreachable