[atomics.ref.generic] Avoid use of undeclared 'T'

Fixes NB US 192-312 (C++26 CD).

Author: jensmaurer

source/threads.tex

@@ -3674,7 +3674,7 @@
 \pnum
 The program is ill-formed
 if \tcode{is_always_lock_free} is \tcode{false} and
-\tcode{is_volatile_v<T>} is \tcode{true}.
+\tcode{is_volatile_v<\placeholder{integral-type}>} is \tcode{true}.
 
 \begin{codeblock}
 namespace std {
@@ -3892,7 +3892,7 @@
 \pnum
 The program is ill-formed
 if \tcode{is_always_lock_free} is \tcode{false} and
-\tcode{is_volatile_v<T>} is \tcode{true}.
+\tcode{is_volatile_v<\placeholder{floating-point-type}>} is \tcode{true}.
 
 \begin{codeblock}
 namespace std {
@@ -4180,7 +4180,7 @@
 \pnum
 The program is ill-formed
 if \tcode{is_always_lock_free} is \tcode{false} and
-\tcode{is_volatile_v<T>} is \tcode{true}.
+\tcode{is_volatile_v<\placeholder{pointer-type}>} is \tcode{true}.
 
 \begin{codeblock}
 namespace std {