WIP: Fail tests for calls to console.warn()

What does this MR do?

This is a workaround for making sure we catch all Bootstrap-Vue warnings in our tests.

Bootstrap-Vue currently does not support configuring a custom warn handler.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/53730

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.