Apply suggestions from code review

Co-authored-by: Daniel Jünger <2955913+sleeepyjack@users.noreply.github.com>

include/cuco/detail/static_multiset/static_multiset_ref.inl

@@ -501,7 +501,7 @@ class operator_impl<
   }
 
   /**
-   * @brief Counts the occurrence of a given key contained in multiset
+   * @brief Counts the occurrence of a given key contained in the multiset
    *
    * @note If the given key has no match, the first rank of the group will
    * return 1, other threads will return 0.