Fix runner form fields test by waiting on async components

What does this MR do and why?

Fix runner form fields test by waiting on async components, this fix this test in Vue 3

References

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• Fix jest tests in spec/frontend/ci/runner for V... (#503489 - closed)

MR acceptance checklist

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How to set up and validate locally

VUE_VERSION=3 yarn jest ee/spec/frontend/ci/runner/components/runner_form_fields_spec.js

Related to #503489 (closed)