py/runtime: Fix bool unary op for subclasses of native types.

Previously a subclass of a type that didn't implement unary_op, or didn't
handle MP_UNARY_OP_BOOL, would raise TypeError on bool conversion.

Fixes #5677.

tests/basics/unary_op.py

@@ -23,5 +23,12 @@ print(not A())
 # check user instances derived from builtins
 class B(int): pass
 print(not B())
+print(True if B() else False)
 class C(list): pass
 print(not C())
+print(True if C() else False)
+# type doesn't define unary_op
+class D(type): pass
+d = D("foo", (), {})
+print(not d)
+print(True if d else False)