Only require year in Gergorian `inLeapYear` method
Only require year in Gergorian `inLeapYear` method

A later commit is going to type all inLeapYear methods
as only needing the year in the input, not a full date.
This inLeapYear implementation is the only one where
this type limitation needed a runtime change, so it's
split into its own commit.

js-temporal/temporal-polyfill,js-temporal/temporal-polyfill,js-temporal/temporal-polyfill