fix an import warning in test_doctest.py when importing readline in WASI

Author: graingert

Lib/test/test_doctest/test_doctest.py

@@ -2869,6 +2869,12 @@ def get_data(self, path):
         with open(path, mode='rb') as f:
             return f.read()
 
+    def exec_module(self, module):
+        raise ImportError
+
+    def create_module(self, spec):
+        return None
+
 class TestHook:
 
     def __init__(self, pathdir):