[3.13] gh-141612: improve test_trampoline_works_with_forks coverage (GH-141613) (#141826)

* gh-141612: improve `test_trampoline_works_with_forks` coverage (#141613)

(cherry picked from commit f15f6d0ba3)

Lib/test/test_perf_profiler.py

@@ -157,6 +157,16 @@ class TestPerfTrampoline(unittest.TestCase):
         self.assertIn(f"py::bar_fork:{script}", child_perf_file_contents)
         self.assertIn(f"py::baz_fork:{script}", child_perf_file_contents)
 
+        # The parent's map should not contain the child's symbols.
+        self.assertNotIn(f"py::foo_fork:{script}", perf_file_contents)
+        self.assertNotIn(f"py::bar_fork:{script}", perf_file_contents)
+        self.assertNotIn(f"py::baz_fork:{script}", perf_file_contents)
+
+        # The child's map should not contain the parent's symbols.
+        self.assertNotIn(f"py::foo:{script}", child_perf_file_contents)
+        self.assertNotIn(f"py::bar:{script}", child_perf_file_contents)
+        self.assertNotIn(f"py::baz:{script}", child_perf_file_contents)
+
     def test_sys_api(self):
         code = """if 1:
                 import sys