Replace class "js-builds-dropdown-list" in favor of a data-testid selector

Description

Currently the .js-builds-dropdown-list class is only used in specs such as:

• spec/features/projects/pipelines/pipelines_spec.rb

This class should be replaced by a [data-testid=...] style selector in our tests.

Note: This class is mostly used by the mini pipeline in the commit page, see more at #300403 (closed)