[streambuf.virt.put] Replace "effects" with "affects" in footnote (#8329)

Fixes NB US 188-303 (C++26 CD).

Author: eisenwave

source/iostreams.tex

@@ -4058,7 +4058,7 @@
 That is, for each class derived from a specialization of
 \tcode{basic_streambuf}
 in this Clause\iref{stringbuf,filebuf},
-a specification of how consuming a character effects the associated output sequence is given.
+a specification of how consuming a character affects the associated output sequence is given.
 There is no requirement on a program-defined class.
 \end{footnote}
 \item