New type analyzer: confusing error message for broken named tuple

[ilevkivskyi]

This test case fails:

[case testInvalidNamedTupleBaseClass]
from typing import NamedTuple

defer: Yes

class A(NamedTuple('N', [1])): pass # E: Tuple expected as NamedTuple() field

class Yes: ...

because there is a spurious additional error

main:5: error: Name 'namedtuple@5' already defined on line 5

See also #6422 that may be related (broken named tuples, and named tuples at function scope use similar logic).