Fix flaky pipelines spec

Previously this test would attempt to play a job, but it did not
actually wait for the request to be sent.  Now we wait for the
transition from spinner back to play icon to ensure the request to
`JobsController#play` has completed.

This is similar to
https://gitlab.com/gitlab-org/gitlab/-/issues/362880 and fix in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/101728.

Relates to
https://gitlab.com/gitlab-org/quality/engineering-productivity/master-broken-incidents/-/issues/4