[3.14] gh-94242: Clarify comments for _MAX_WINDOWS_WORKERS in concurrent.futures.process (GH-135537) (#156906)

gh-94242: Clarify comments for _MAX_WINDOWS_WORKERS in concurrent.futures.process (GH-135537)
(cherry picked from commit c8ea867)

Co-authored-by: An Long <aisk@users.noreply.github.com>

Author: miss-islington

Lib/concurrent/futures/process.py

@@ -119,10 +119,11 @@ def _python_exit():
 
 
 # On Windows, WaitForMultipleObjects is used to wait for processes to finish.
-# It can wait on, at most, 63 objects. There is an overhead of two objects:
+# It can wait on, at most, 64 objects. There is an overhead of three objects:
 # - the result queue reader
 # - the thread wakeup reader
-_MAX_WINDOWS_WORKERS = 63 - 2
+# - the SIGINT handler
+_MAX_WINDOWS_WORKERS = 64 - 3
 
 # Hack to embed stringification of remote traceback in local traceback