Fix spec violations in blob_button_group_spec

What does this MR do and why?

In regards of epic &5102, this MR fixes the following spec violations in spec/frontend/repository/components/blob_button_group_spec.js #391071 (closed):

• spying on methods

How to set up and validate locally

Run tests:

yarn jest spec/frontend/repository/components/blob_button_group_spec.js

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes #391071 (closed)