[library.general,tab:thread.summary] Update references to renamed Clause (#6149)

Author: JohelEGP

source/lib-intro.tex

@@ -121,7 +121,7 @@
 The regular expressions library\iref{re} provides regular expression matching and searching.
 
 \pnum
-The thread support library\iref{thread} provides components to create
+The concurrency support library\iref{thread} provides components to create
 and manage threads,
 including atomic operations, mutual exclusion, and interthread communication.
 

source/threads.tex

@@ -9,7 +9,7 @@
 and values
 between threads, as summarized in \tref{thread.summary}.
 
-\begin{libsumtab}{Thread support library summary}{thread.summary}
+\begin{libsumtab}{Concurrency support library summary}{thread.summary}
 \ref{thread.req}      & Requirements          &                               \\ \rowsep
 \ref{thread.stoptoken}& Stop tokens           & \tcode{<stop_token>}          \\ \rowsep
 \ref{thread.threads}  & Threads               & \tcode{<thread>}              \\ \rowsep