Null coalescing assignment operator in if condition does not remove null from type

[M393]

https://psalm.dev/r/cdff4f688e
All three functions should be without a warning as they all behave the same.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/cdff4f688e

<?php
function f(): object|null {
    return null;
}
function a(object|null $s): object {
    if (!($s ??= f())) {
        exit;
    }
    return $s;
}
function b(object|null $s): object {
    if (!$s && !($s = f())) {
        exit;
    }
    return $s;
}
function c(object|null $s): object {
    $s ??= f();
    if (!$s) {
        exit;
    }
    return $s;
}

Psalm output (using commit 03ee02c):

ERROR: NullableReturnStatement - 9:12 - The declared return type 'object' for a is not nullable, but the function returns 'null|object'

ERROR: InvalidNullableReturnType - 5:29 - The declared return type 'object' for a is not nullable, but 'null|object' contains null