Add NEWS entry for gh-87512

Co-authored-by: Claude Opus 4.5 <[email protected]>

Author: gpshead

Misc/NEWS.d/next/Library/2025-11-29-03-02-45.gh-issue-87512.bn4xbm.rst

@@ -0,0 +1,5 @@
+Fix :func:`subprocess.Popen.communicate` timeout handling on Windows
+when writing large input. Previously, the timeout was ignored during
+stdin writing, causing the method to block indefinitely if the child
+process did not consume input quickly. The stdin write is now performed
+in a background thread, allowing the timeout to be properly enforced.