[FIX] web_editor: properly hide the custom colors section if needed

The 'custom' key was not working anymore as a key to exclude the
ability to choose a custom color from a color palette widget. It was
thus appearing for choosing the transparent color for over-the-content
headers... which is not possible to save right now.

Part of https://github.com/odoo/odoo/pull/65139

closes odoo/odoo#65154

X-original-commit: 8f9eb57df5c6a253ee0702c0e1fb2016cab7eb1e
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/wysiwyg/widgets/color_palette.js

@@ -136,14 +136,17 @@ const ColorPaletteWidget = Widget.extend({
         this._markSelectedColor();
 
         // Colorpicker
-        let defaultColor = this.selectedColor;
-        if (defaultColor && !ColorpickerWidget.isCSSColor(defaultColor)) {
-            defaultColor = weUtils.getCSSVariableValue(defaultColor, this.style);
+        if (!this.options.excluded.includes('custom')) {
+            let defaultColor = this.selectedColor;
+            if (defaultColor && !ColorpickerWidget.isCSSColor(defaultColor)) {
+                defaultColor = weUtils.getCSSVariableValue(defaultColor, this.style);
+            }
+            this.colorPicker = new ColorpickerWidget(this, {
+                defaultColor: defaultColor,
+            });
+            await this.colorPicker.prependTo($colorSection);
         }
-        this.colorPicker = new ColorpickerWidget(this, {
-            defaultColor: defaultColor,
-        });
-        await this.colorPicker.prependTo($colorSection);
+
         return res;
     },
     /**