Cleanup geometry validation dock before QgsApplication exit

Refs #20283, possibly fixes it

Author: nyalldawson

src/app/qgisapp.cpp

@@ -1584,6 +1584,8 @@ QgisApp::~QgisApp()
   mBrowserWidget2 = nullptr;
   delete mBrowserModel;
   mBrowserModel = nullptr;
+  delete mGeometryValidationDock;
+  mGeometryValidationDock = nullptr;
 
   QgsGui::instance()->nativePlatformInterface()->cleanup();