fix(combobox): removed unnecessary undefined type for combobox onValu…

[Powerplex]

…eChange

TASK: #2208

Description, Motivation and Context

onValueChange accepted string | undefined as a first parameter in its callback (single selection mode only).

It means that our consumer are forced to check the type:

<Combobox value={value} onValueChange={(value)  => {
  if (value !== undefined) setValue(value)
}}

But I think such a case can't happen. Once a Combobox is controlled, its value must remain a string.

Types of changes

• [x] 🪲 Bug fix (non-breaking change which fixes an issue)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.63%. Comparing base (2d2e366) to head (568b5a7). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2209 +/- ## ======================================= Coverage 97.63% 97.63% ======================================= Files 753 753 Lines 5925 5925 Branches 2086 2119 +33 ======================================= Hits 5785 5785 Misses 138 138 Partials 2 2 ```

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