[FIX] survey: correctly fade out wrong answer bars in session mode

This commit fixes the faded out answers bars on choice questions during a
survey session.
The logic is currently inverted (correct answers are faded out instead of wrong
ones).

LINKS

PR #48442
Task 2208574

addons/survey/static/src/js/survey_session_chart.js

@@ -199,8 +199,8 @@ publicWidget.registry.SurveySessionChart = publicWidget.Widget.extend({
     _getBackgroundColor: function (metaData) {
         var opacity = '0.8';
         if (this.showAnswers && this.hasCorrectAnswers) {
-            if (this._isValidAnswer(metaData.dataIndex)){
-                opacity = 0.3;
+            if (!this._isValidAnswer(metaData.dataIndex)){
+                opacity = '0.3';
             }
         }
         var rgb = SESSION_CHART_COLORS[metaData.dataIndex];