[class.pre] Adjust phrasing around 'identifer'

Fixes NB CA-083 (C++26 CD).

Author: jensmaurer

source/classes.tex

@@ -131,7 +131,7 @@
 within a single \grammarterm{class-property-specifier-seq}.
 Whenever a \grammarterm{class-key} is followed
 by a \grammarterm{class-head-name},
-the identifier \tcode{final}, \tcode{trivially_relocatable_if_eligible},
+one of the identifiers \tcode{final}, \tcode{trivially_relocatable_if_eligible},
 or \tcode{replaceable_if_eligible}, and a colon or left brace,
 the identifier is interpreted as a \grammarterm{class-property-specifier}.
 \begin{example}