add test to assign non-string keys to a function's __dict__

Author: cosminbasca

graalpython/com.oracle.graal.python.test/src/tests/test_dict.py

@@ -435,3 +435,10 @@ class Foo(object):
     f.__dict__[1] = 1
     f.a = 'a'
     assert f.__dict__ == {1: 1, 'a': 'a'}
+
+    def bar():
+        pass
+
+    bar.__dict__[1] = 1
+    bar.a = 'a'
+    assert bar.__dict__ == {1: 1, 'a': 'a'}