(chore) Add test coverage for the NumberField component

Requirements

[ ] This PR has a title that briefly describes the work done including the ticket number. If there is a ticket, make sure your PR title includes a conventional commit label. See existing PR titles for inspiration.
[ ] My work conforms to the OpenMRS 3.0 Styleguide and design documentation.
[ ] My work includes tests or is validated by existing tests.

Add test coverage for the NumberField component