proto_sync: improve error message. (#8527)
proto_sync: improve error message. (#8527)

It was previously pointing at proto_sync.py, which is misleading, it's
necessary to run the full tools/proto_format.sh for a proto fix.

Signed-off-by: Harvey Tuch <c185081708e02336640916420d0c772668570de5@google.com>
jrajahalme/envoy,eklitzke/envoy,lyft/envoy,lyft/envoy,eklitzke/envoy,lizan/envoy,istio/envoy,envoyproxy/envoy,lizan/envoy,eklitzke/envoy,istio/envoy,lyft/envoy,lizan/envoy,eklitzke/envoy,lyft/envoy,lizan/envoy,lizan/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lyft/envoy,envoyproxy/envoy-wasm,istio/envoy,jrajahalme/envoy,envoyproxy/envoy,istio/envoy,eklitzke/envoy,lyft/envoy,envoyproxy/envoy-wasm,istio/envoy,eklitzke/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,istio/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,jrajahalme/envoy,envoyproxy/envoy,jrajahalme/envoy