frontend: Fix build with Qt 6.12

After Qt upstream commit 556028d16a0 [1], 'QHash' and 'QSet' need
to be explicitly included when using 'QT_ENABLE_STRICT_MODE_UP_TO'.

1. https://code.qt.io/cgit/qt/qtbase.git/commit/?id=556028d16a059006cc5a03676260aff5428b767e

Signed-off-by: Jimi Huotari <chiitoo@gentoo.org>

frontend/OBSApp.hpp

@@ -29,6 +29,7 @@
 
 #include <QAbstractNativeEventFilter>
 #include <QApplication>
+#include <QHash>
 #include <QPalette>
 #include <QPointer>
 #include <QUuid>

frontend/OBSApp_Themes.cpp

@@ -31,6 +31,7 @@
 #include <QFileSystemWatcher>
 #include <QMetaEnum>
 #include <QRandomGenerator>
+#include <QSet>
 #include <QTimer>
 
 using namespace std;