[util.smartptr.shared.cast] Add hyphen for 'well-formed'.

Fixes NB JP 007 (C++20 DIS)

Author: jensmaurer

source/utilities.tex

@@ -10851,7 +10851,7 @@
 \pnum
 \mandates
 The expression \tcode{dynamic_cast<T*>((U*)nullptr)} is well-formed.
-The expression \tcode{dynamic_cast<typename shared_ptr<T>::element_type*>(r.get())} is well formed.
+The expression \tcode{dynamic_cast<typename shared_ptr<T>::element_type*>(r.get())} is well-formed.
 
 \pnum
 \expects