[specialized.algorithms] Fix a typo: iter_difference_t<T> -> iter_difference_t<I> (#8143)

A misapplication of P3179R9.

Author: dmitriy-sobolev

source/algorithms.tex

@@ -13684,7 +13684,7 @@
 A type \tcode{I} models \exposconcept{nothrow-random-access-iterator}
 only if no exceptions are thrown from comparisons of valid iterators,
 or the \tcode{-}, \tcode{+}, \tcode{-=}, \tcode{+=}, \tcode{[]} operators
-on valid values of type \tcode{I} and \tcode{iter_difference_t<T>}.
+on valid values of type \tcode{I} and \tcode{iter_difference_t<I>}.
 \begin{note}
 This concept allows some \libconcept{random_access_iterator}\iref{iterator.concept.random.access}
 operations to throw exceptions.