PermissionManager::missingPermissionError takes a $short parameter that is meant to return early and not build an expensive error for "quick" permission checks that just need a boolean and don't need to display the error anywhere:
// We avoid expensive display logic for quickUserCan's and such
It stopped doing the early return in 1.43 because the line
return [ 'badaccess-group0' ];
was replaced with
$status->fatal( 'badaccess-group0' );
which no longer has a return, and continues on with the expensive error creation later in the function, even though it doesn't use it.
I *think* the fix is as simple as changing to
return $status->fatal( 'badaccess-group0' );
@matmarex can you confirm?