remove old types when both side of a ternary reassign a variable

[orklah]

https://psalm.dev/r/198b6a7c3a
$_a in this example should not contain null

https://psalm.dev/r/705d3062f6
This edge case could be interesting to check also

PHPStan infers the correct type

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/198b6a7c3a

<?php
$_a = null;
$b = rand(0,1) ? '' : 'true';
$b === 'true' ? $_a = 'Y' : $_a = 'N';

/** @psalm-trace $_a */

Psalm output (using commit eb973ab):

INFO: Trace - 6:24 - $_a: "N"|"Y"|null

https://psalm.dev/r/705d3062f6

<?php
$_a = rand(0,1) ? '' : 'true';
$_a === 'true' ? $_a = 'Y' : $_a = 'N';

/** @psalm-trace $_a */

Psalm output (using commit eb973ab):

INFO: Trace - 5:24 - $_a: ""|"N"|"Y"|"true"