The GitLab UI update changed the spinner selector from `spinner` to
`gl-spinner`, so we need to update it, so that our tests won't fail.

It will be hooked up to the markdown editor later

Update dependency @gitlab/ui to ^5.7.1

See merge request gitlab-org/gitlab-ce!31026

This fixes fill colors not working with Mermaid and pulls
in a number of other fixes.

* https://github.com/knsv/mermaid/blob/master/CHANGELOG.md
* https://github.com/knsv/mermaid/#special-note-regarding-version-82

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64601

Removed stylelint-error-string-formatter
 as this was having a circular reference fail

This is needed to fix an issue where updating to the latest Webpack
causes an acorn dependency error:
https://github.com/webpack-contrib/webpack-bundle-analyzer/issues/245

Seen while trying to update dependencies for Mermaid in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30985

Moved the block that fails tests on unmocked axios requests from
test_setup to its own mock, and added a jQuery mock that fails
tests if they use unmocked $.ajax().