Mock data improvements in related issuable components

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The following discussions from !9730 (merged) should be addressed:

• @winh started a discussion:

  Can we create a follow-up issue to

  • use a dynamic fixture for the mock data, so we make sure it matches the backend endpoint
  • rename the mocks to something that tells more about their content that issuableX

• @winh started a discussion:

  There seems to be no test for canRemove: false here. 🤔