Fix additional unused async in spec/frontend and update eslint config

What does this MR do and why?

Fix async functions with no await in some jest runner tests.

Implements last part of #406588 (closed)

Related: #397674 (closed), gitlab-org/frontend/eslint-plugin#13

Screenshots or screen recordings

NA

How to set up and validate locally

The pipeline should pass, see the new entry at .eslintrc.yml.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #406588 (closed)