Correct icon_margin_scale for fold indicator (#3003)

Fixes a design regression on Preview where the fold icon became small
due to the icon standardization PR.

Release Notes:

- [Preview] Fixed an issue with the size of the fold line icon.

styles/src/style_tree/editor.ts

@@ -91,7 +91,7 @@ export default function editor(): any {
             vertical_scale: 0.55,
         },
         folds: {
-            icon_margin_scale: 2.5,
+            icon_margin_scale: 4,
             folded_icon: "icons/chevron_right.svg",
             foldable_icon: "icons/chevron_down.svg",
             indicator: toggleable({