Darwin: Capture 'this' via '&' instead of '=' to fix build with C++20

qdarwinpermissionplugin.mm:37:35: error: implicit capture of 'this'
with a capture default of '=' is deprecated [-Werror,-Wdeprecated-this-capture]

Pick-to: 6.8
Change-Id: I05afd05f43ddceb88cb5fffd85959b494c29ce6a
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/corelib/platform/darwin/qdarwinpermissionplugin.mm

@@ -28,7 +28,7 @@
         return;
     }
 
-    [m_handler requestPermission:permission withCallback:[=](Qt::PermissionStatus status) {
+    [m_handler requestPermission:permission withCallback:[&](Qt::PermissionStatus status) {
         // In case the callback comes in on a secondary thread we need to marshal it
         // back to the main thread. And if it doesn't, we still want to propagate it
         // via an event, to avoid any GCD locks deadlocking the application on iOS