test: increase coverage on FilterableMultiSelect (#17763)

* test: adding comment to run codecov

* test: still 68% :-'(

* test: its 74%

* test: removed comments

* test: added more tests, still at 75.2%

* test: coverage hit 89 :-))))))

* test: added some tests for focus

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Co-authored-by: andrew <[email protected]>
Co-authored-by: Taylor Jones <[email protected]>