Add missing override on destructor

src/folder/foldertreewidget.h

@@ -55,7 +55,7 @@ public:
     explicit FolderTreeWidget(
         QWidget *parent = nullptr, KXMLGUIClient *xmlGuiClient = nullptr, TreeViewOptions options = (TreeViewOptions)(ShowUnreadCount
                                                                                                                       |ShowCollectionStatisticAnimation), FolderTreeWidgetProxyModel::FolderTreeWidgetProxyModelOptions optReadableProxy = FolderTreeWidgetProxyModel::None);
-    ~FolderTreeWidget();
+    ~FolderTreeWidget() override;
 
     /**
      * The possible tooltip display policies.

src/search/widgethandler/messagerulewidgethandler.h

@@ -17,7 +17,7 @@ public:
     {
     }
 
-    ~MessageRuleWidgetHandler()
+    ~MessageRuleWidgetHandler() override
     {
     }
 

src/snippets/snippetselectattachmentwidget.h

@@ -19,7 +19,7 @@ class MAILCOMMON_TESTS_EXPORT SnippetSelectorWidget : public PimCommon::SimpleSt
     Q_OBJECT
 public:
     explicit SnippetSelectorWidget(QWidget *parent = nullptr);
-    ~SnippetSelectorWidget();
+    ~SnippetSelectorWidget() override;
 
     void addNewEntry() override;
     QString customEntry(const QString &text) override;