Qt: Retranslate GameList header and Filter line

Didn't notice this until I was trying to change the default font
to Comic Sans MS when language is set to English in yuzu.

src/citra_qt/game_list.h

@@ -107,6 +107,9 @@ private:
 
     QString FindGameByProgramID(QStandardItem* current_item, u64 program_id, int role);
 
+    void changeEvent(QEvent*) override;
+    void RetranslateUI();
+
     GameListSearchField* search_field;
     GMainWindow* main_window = nullptr;
     QVBoxLayout* layout = nullptr;