fix(serverless-scheduler-proxy): use golang:1.18-alpine (#3519)
fix(serverless-scheduler-proxy): use golang:1.18-alpine (#3519)

* fix(serverless-scheduler-proxy): use golang:1.18-alpine

* intentionally using 1.13

* actually use 1.18
googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots