QNetworkInformation: Add missing \since marker

The new name was introduced in 6.4, but the documentation stayed the
same since it was initially written.

Amends 8367be8ede

Pick-to: 6.4
Change-Id: Idb27b551760f0d0cb41220be18a4d87e5875baae
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/kernel/qnetworkinformation.cpp

@@ -675,6 +675,7 @@ bool QNetworkInformation::load(QStringView backend)
 #endif // QT_DEPRECATED_SINCE(6,4)
 
 /*!
+    \since 6.4
     Load a backend which supports \a features.
 
     Returns \c true if it managed to load the requested backend or