ci: cache build artifact across runs (#1343)
ci: cache build artifact across runs (#1343)

Description: Updates build job to use cached library artifact when run on the same SHA, allowing retries for connectivity failure or flakiness to run much faster.
Risk Level: Low
Testing: CI

Signed-off-by: Mike Schore <270e364e708f2af319f244c09ceba52a03dbd980@gmail.com>
envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile