fix: use React 18 and 19 compatible types

[angeloashmore]

Types of changes

• Chore (a non-breaking change which is related to package maintenance)
• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR updates @prismicio/next to be compatible with React 18 and 19 TypeScript types.

React 19 requires changing JSX.Element to React.JSX.Element (see the React 19 release notes). The change is compatible with React 18's TypeScript types.

Checklist:

• My change requires an update to the official documentation.
• All TSDoc comments are up-to-date and new ones have been added where necessary.
• All new and existing tests are passing.