Change build status badge to use GitHub Actions

Author: dhui

README.md

@@ -1,4 +1,4 @@
-[![CircleCI - Build Status](https://img.shields.io/circleci/build/github/golang-migrate/migrate/master)](https://circleci.com/gh/golang-migrate/migrate)
+[![GitHub Workflow Status (branch)](https://img.shields.io/github/workflow/status/golang-migrate/migrate/CI/master)](https://github.com/golang-migrate/migrate/actions/workflows/ci.yaml?query=branch%3Amaster)
 [![GoDoc](https://pkg.go.dev/badge/github.com/golang-migrate/migrate)](https://pkg.go.dev/github.com/golang-migrate/migrate/v4)
 [![Coverage Status](https://img.shields.io/coveralls/github/golang-migrate/migrate/master.svg)](https://coveralls.io/github/golang-migrate/migrate?branch=master)
 [![packagecloud.io](https://img.shields.io/badge/deb-packagecloud.io-844fec.svg)](https://packagecloud.io/golang-migrate/migrate?filter=debs)