PY-20983 (partial fix): do not break if python target is module.

This fix is critical anyway, because running module as python is common

python/testData/testRunner/env/runModuleAsFile/unittests/stubs.py

@@ -0,0 +1 @@
+A = 1

python/testData/testRunner/env/runModuleAsFile/unittests/test_some_class.py

@@ -0,0 +1,9 @@
+import unittest
+
+from .stubs import A
+
+class TestSomeClass(unittest.TestCase):
+    def test_some_class(self):
+        some_class = A
+        pass
+