(fix) Reworked logic for gravida calculation

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[x] 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.

This PR corrects the gravida calculation logic within the form engine.