[ADF-3558] Fix failing test for unshare file (#3786)

e2e/content-services/unshare_file.e2e.ts

@@ -94,5 +94,6 @@ describe('Unshare file', () => {
         browser.get(sharedLink);
 
         errorPage.checkErrorPage();
+        errorPage.checkBackButton();
     });
 });

e2e/pages/adf/errorPage.js

@@ -67,6 +67,10 @@ var ErrorPage = function(){
         return errorPageDescription.getText();
     };
 
+    this.checkBackButton = function () {
+        return Util.waitUntilElementIsVisible(backButton);
+    };
+
 };
 
 module.exports = ErrorPage;