Fix Time#change when used with :usec and offset times

This is a follow-up of #16758 and the branch is based on it.

Fixes #16759.
@pixeltrix I opened a 2nd PR (about the `:nspec` option): https://github.com/rails/rails/pull/16758 (it is based on the branch of the 1st PR).

Sorry for the spam and thanks for the help! :bow: