py/obj: Accept user types in mp_obj_get_int_maybe.

This is possible now that MP_UNARY_OP_INT_MAYBE exists.

As a consequence mp_obj_get_int now also supports user types, which was
previously possible with MP_UNARY_OP_INT but no tests existed for it.

Signed-off-by: Damien George <damien@micropython.org>

tests/basics/string_format_modulo.py

@@ -13,6 +13,12 @@ print("=%s=" % [1, 2])
 print("=%s=" % "str")
 print("=%r=" % "str")
 
+# test calling __int__
+class A:
+    def __int__(self):
+        return 123
+print("%d" % A())
+
 try:
     print("=%s=%s=" % 1)
 except TypeError: