[3.12] gh-109292: add symtable impact of PEP 709 to What's New (GH-109293) (#109296)

gh-109292: add symtable impact of PEP 709 to What's New (GH-109293)
(cherry picked from commit 2b1e2f1)

Co-authored-by: Carl Meyer <[email protected]>

Author: miss-islington

Doc/whatsnew/3.12.rst

@@ -258,6 +258,9 @@ Inlining does result in a few visible behavior changes:
 
 * There is no longer a separate frame for the comprehension in tracebacks,
   and tracing/profiling no longer shows the comprehension as a function call.
+* The :mod:`symtable` module will no longer produce child symbol tables for each
+  comprehension; instead, the comprehension's locals will be included in the
+  parent function's symbol table.
 * Calling :func:`locals` inside a comprehension now includes variables
   from outside the comprehension, and no longer includes the synthetic ``.0``
   variable for the comprehension "argument".