[readme] replace runkit CI badge with shields.io check-runs badge

Author: ljharb

README.md

@@ -33,5 +33,5 @@ if (typeof AsyncIterator === 'function') {
 [downloads-url]: https://npm-stat.com/charts.html?package=asynciterator.prototype
 [codecov-image]: https://codecov.io/gh/ljharb/AsyncIterator.prototype/branch/main/graphs/badge.svg
 [codecov-url]: https://app.codecov.io/gh/ljharb/AsyncIterator.prototype/
-[actions-image]: https://img.shields.io/endpoint?url=https://github-actions-badge-u3jn4tfpocch.runkit.sh/ljharb/AsyncIterator.prototype
+[actions-image]: https://img.shields.io/github/check-runs/ljharb/AsyncIterator.prototype/main
 [actions-url]: https://github.com/AsyncIterator/iterator.prototype/actions