tests/basics/int_big1.py: Add test for big int in mp_obj_get_int_maybe.

tests/basics/int_big1.py

@@ -99,3 +99,7 @@ x = -4611686018427387904 # big
 # sys.maxsize is a constant mpz, so test it's compatible with dynamic ones
 import sys
 print(sys.maxsize + 1 - 1 == sys.maxsize)
+
+# test extraction of big int value via mp_obj_get_int_maybe
+x = 1 << 70
+print('a' * (x + 4 - x))