Add a test for searching in marker's categories

In #3299, searching for the marker's categories was implemented, but not test was added because it was a bit too difficult for a contributor.

New tests will be in `src/test/store/profile-view.test.js`, around `describe('changeMarkersSearchString')`. However our current tests don't make it easy to use some non-zero categories for markers, so we need to change how we add markers to profiles in tests.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-384)