fix: handle boolean css var (#2350)

#2324

Author: dummdidumm

packages/svelte2tsx/src/htmlxtojsx_v2/nodes/Attribute.ts

@@ -94,7 +94,7 @@ export function handleAttribute(
                   element.addAttribute(name, value);
               }
             : (name: TransformationArray, value?: TransformationArray) => {
-                  if (attr.name.startsWith('--') && attr.value !== true) {
+                  if (attr.name.startsWith('--')) {
                       // CSS custom properties are not part of the props
                       // definition, so wrap them to not get "--xx is invalid prop" errors
                       name.unshift('...__sveltets_2_cssProp({');

packages/svelte2tsx/test/htmlx2jsx/samples/custom-css-properties/expectedv2.js

@@ -4,4 +4,5 @@
   betweenprop
   --custom-css-property3="hi{jo}hi"
   --custom-css-property4='hi{jo}hi'
-  --custom-css-property5=hi{jo}hi />
+  --custom-css-property5=hi{jo}hi
+  --custom-css-property6 />