[FIX] web_editor: fix forward-port

Forward-port of https://github.com/odoo/odoo/commit/227fc6408ddc998529bb1c38222ddba50f40868b
made with https://github.com/odoo/odoo/commit/717f4583949219c346c87c390fbc336b4f31571c
introduced a JS error.

closes odoo/odoo#28187

addons/web_editor/static/src/js/editor/snippets.options.js

@@ -834,7 +834,7 @@ registry.colorpicker = SnippetOption.extend({
      */
     _onColorResetButtonClick: function () {
         this.$target.removeClass(this.classes);
-        self.$target.trigger('content_changed');
+        this.$target.trigger('content_changed');
         this.$el.find('.colorpicker button.selected').removeClass('selected');
     },
 });