Core: Use override consistently

clang-tidy fixes from modernize-use-override check.

Change-Id: If33399d60e96cae766bbedbe30044ada411e862f
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/documentmanager.h

@@ -157,11 +157,11 @@ signals:
     void projectsDirectoryChanged(const Utils::FileName &directory);
 
 protected:
-    bool eventFilter(QObject *obj, QEvent *e);
+    bool eventFilter(QObject *obj, QEvent *e) override;
 
 private:
     explicit DocumentManager(QObject *parent);
-    ~DocumentManager();
+    ~DocumentManager() override;
 
     void documentDestroyed(QObject *obj);
     void checkForNewFileName();