if this is by design i'm fine with somebody closing this issue.

i've not found mention of such case in pep so i though it's not by design.
docs say `assert` just takes "expression" and "assignment expression" has "expression" in it's name.
https://docs.python.org/3/reference/simple_stmts.html#the-assert-statement

workaraund does not look as cool because of parentheses.

again, if this is "as intended" i'm fine with closing issue.