Add flush=True before os._exit and add NEWS entry

os._exit() does not flush Python IO buffers, so the print(os.getpid())
output was lost when stdout is piped. Add flush=True to ensure the
child PID reaches the parent.

Also add the required NEWS entry.

<claude>

Author: yonatan-genai

Lib/test/test_perf_profiler.py

@@ -116,7 +116,7 @@ def baz_fork():
                 def foo():
                     pid = os.fork()
                     if pid == 0:
-                        print(os.getpid())
+                        print(os.getpid(), flush=True)
                         baz_fork()
                         os._exit(0)
                     else:

Misc/NEWS.d/next/Tests/2026-04-04-00-00-00.gh-issue-144766.Yk3mPq.rst

@@ -0,0 +1,4 @@
+Fix flaky :func:`test_trampoline_works_with_forks` by using ``os._exit(0)``
+in the fork child to avoid fragile Python finalization, and by flushing
+stdout before exit. Also fix the parent's wait status handling to use
+``os.WEXITSTATUS()``.