Add comment about deferred import

Author: ADThomas-astro

Lib/test/test_pdb.py

@@ -16,6 +16,7 @@
 from contextlib import ExitStack, redirect_stdout
 from io import StringIO
 from test import support
+# Deferred import: from test.test_repl import spawn_repl
 from test.support import force_not_colorized, os_helper
 from test.support.import_helper import import_module
 from test.support.pty_helper import run_pty, FakeInput