gh-119070: Avoid test crash due to Unicode in stderr output (GH-119747)

Author: zooba

Lib/test/test_launcher.py

@@ -232,7 +232,7 @@ def run_py(self, args, env=None, allow_fail=False, expect_returncode=0, argv=Non
             p.stdin.close()
             p.wait(10)
             out = p.stdout.read().decode("utf-8", "replace")
-            err = p.stderr.read().decode("ascii", "replace")
+            err = p.stderr.read().decode("ascii", "replace").replace("\uFFFD", "?")
         if p.returncode != expect_returncode and support.verbose and not allow_fail:
             print("++ COMMAND ++")
             print([self.py_exe, *args])