This PR fixes an error that occurs when adding a new lineitem to a contribution.
This issue is caused by an invalid Type operation at https://lab.civicrm.org/extensions/lineitemedit/-/blob/master/CRM/Lineitemedit/Util.php#L510
$updatedAmount = "40.0"
CRM_Utils_Array::value('fee_amount', $updatedContribution, 0) = ""
It would try to do
"40.0" - "", This would only throw a notice in PHP7.4 and treat the empty string as 0, but in PHP8.0+ this is not valid and would throw the error Error: Uncaught TypeError: Unsupported operand types: string - string.
8.0 and CiviCRM