$ cat >ruf033_1.py <<'# EOF'
from dataclasses import dataclass
@dataclass
class Foo:
    def __post_init__(self, bar: int = (x := 1)) -> None:
        pass
# EOF

$ ruff check --isolated ruf033_1.py --select RUF033 --unsafe-fixes --diff 2>&1 | grep error:
error: Fix introduced a syntax error. Reverting all changes.

$ cat >ruf033_2.py <<'# EOF'
from dataclasses import dataclass
@dataclass
class Foo:
    def __post_init__(self, bar: int = (-
        1
    )) -> None:
        pass
# EOF

$ ruff check --isolated ruf033_2.py --select RUF033 --unsafe-fixes --diff 2>&1 | grep error: 
error: Fix introduced a syntax error. Reverting all changes.