[range.zip.transform.iterator] Fix typo in index entry. (cplusplus#7762)

Author: Eelis

source/ranges.tex

@@ -12321,7 +12321,7 @@
 \end{codeblock}
 \end{itemdescr}
 
-\indexlibrarymember{operatorp[]}{zip_transform_view::\exposid{iterator}}%
+\indexlibrarymember{operator[]}{zip_transform_view::\exposid{iterator}}%
 \begin{itemdecl}
 constexpr decltype(auto) operator[](difference_type n) const
   requires @\libconcept{random_access_range}@<@\exposid{Base}@>;