tst_QNetworkReply: port Q_FOREACH to ranged-for

The QHash "cache" isn't modified in the loop body (method is const), in
general cacheSize() shouldn't be susceptible to data races.

Task-number: QTBUG-115839
Change-Id: I122a03ddd5e648d16736c16fa9289eafc886979d
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/network/access/qnetworkreply/tst_qnetworkreply.cpp

@@ -850,7 +850,7 @@ public:
     qint64 cacheSize() const override
     {
         qint64 total = 0;
-        foreach (const CachedContent &entry, cache)
+        for (const auto &[_, entry] : cache.asKeyValueRange())
             total += entry.second.size();
         return total;
     }