leap: Fix loophole in unit tests (#971)
leap: Fix loophole in unit tests (#971)

Currently, it's possible to pass all the unit tests by checking if `(year % 100) == (year % 400)`.

This commit changes one of the test cases so that this is no longer possible. Note that this is a separate issue to #955 -- however, 1996, like 2020, is not divisible by 16, so that loophole will remain closed.
petertseng/x-common,exercism/x-common,jmluy/x-common,rpottsoh/x-common,petertseng/x-common,ErikSchierboom/x-common,jmluy/x-common,exercism/x-common,jmluy/x-common,ErikSchierboom/x-common,rpottsoh/x-common