Even more Qt6 porting

Task-number: QTCREATORBUG-24098
Change-Id: Ib6ef0e521483153c9716c9a1870072e836d6b026
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/languageclient/languageclientsymbolsupport.cpp

@@ -33,6 +33,8 @@
 
 #include <utils/mimetypes/mimedatabase.h>
 
+#include <QFile>
+
 using namespace LanguageServerProtocol;
 
 namespace LanguageClient {