!important in variable value causes Fatal error

[navarr]

With 5.5.1 on PHP 8.4.19

Minimal Less File:

@font-size-md: 20px !important;

.test {
    font-size: @font-size-md;
}

lessc error:

www-data@magento-multisite-php-fpm:/var/www/html$ vendor/bin/lessc test/test.less

Fatal error: Uncaught Error: Attempt to assign property "index" on string in /var/www/html/vendor/wikimedia/less.php/lib/Less/Parser.php:1094
Stack trace:
#0 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Ruleset.php(402): Less_Parser->parseNode('20px !important', Array, 15, Array)
#1 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Ruleset.php(433): Less_Tree_Ruleset->transformDeclaration(Object(Less_Tree_Declaration))
#2 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Ruleset.php(378): Less_Tree_Ruleset->parseValue(Object(Less_Tree_Declaration))
#3 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Variable.php(54): Less_Tree_Ruleset->variable('@font-size-md')
#4 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Expression.php(51): Less_Tree_Variable->compile(Object(Less_Environment))
#5 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Value.php(30): Less_Tree_Expression->compile(Object(Less_Environment))
#6 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Declaration.php(118): Less_Tree_Value->compile(Object(Less_Environment))
#7 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Ruleset.php(109): Less_Tree_Declaration->compile(Object(Less_Environment))
#8 /var/www/html/vendor/wikimedia/less.php/lib/Less/Tree/Ruleset.php(109): Less_Tree_Ruleset->compile(Object(Less_Environment))
#9 /var/www/html/vendor/wikimedia/less.php/lib/Less/Parser.php(241): Less_Tree_Ruleset->compile(Object(Less_Environment))
#10 /var/www/html/vendor/wikimedia/less.php/bin/lessc(198): Less_Parser->getCss()
#11 /var/www/html/vendor/bin/lessc(119): include('/var/www/html/v...')
#12 {main}
  thrown in /var/www/html/vendor/wikimedia/less.php/lib/Less/Parser.php on line 1094