Follow-up from "Make insertCodeSnippetElement find codeblock in the context if not provided"

The following discussion from !4543 (merged) should be addressed:

• @markrian started a discussion: (+1 comment)

  suggestion (non-blocking): WDYT of updating the specs for this helper to make sure it produces a button that matches the DOM created by GlButton? At the moment, the two implementations could get out of sync.

  We should open a follow-up issue for this.