Follow-up from "Fill default suggestion commit message values in the placeholder instead of showing the variable slugs"

The following discussion from !52851 (merged) should be addressed:

• @thomasrandolph started a discussion:

  This whole describe is not good!

  Unfortunately, the way this test suite is set up uses a lot of old, brittle patterns.
  Updating them to facilitate the mocking necessary here (multiple stores, for example) would result in a lot of changes to this file unrelated to this MR.

  I'm opening a follow-up issue to just come back here and update this whole file to use testing patterns more in line with our standards.

tl;dr: The file uses old testing patterns, and should be updated to fully use more standard stuff (@vue/test-utils, etc.)