QBearerEngine: fix const-correctness of a loop with const-propagating QESDP

The loop iterates over a collection of QExplicitSharedDataPointer, which
traditionally doesn't propagate const. In Qt 6, it will, so prepare the
code for this change, by taking the loop variable by non-const reference.

Since the loop is followed by container.clear(), make it a consume-loop
by looping over qExchange(container, {}).

Change-Id: If12ab005544183598fd76a0c486b2df1582710d5
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

src/network/bearer/qbearerengine.cpp

@@ -46,11 +46,10 @@ QT_BEGIN_NAMESPACE
 
 static void cleanUpConfigurations(QHash<QString, QNetworkConfigurationPrivatePointer> &configurations)
 {
-    for (const auto &ptr : qAsConst(configurations)) {
+    for (auto &ptr : qExchange(configurations, {})) {
         ptr->isValid = false;
         ptr->id.clear();
     }
-    configurations.clear();
 }
 
 static bool hasUsedConfiguration(const QHash<QString, QNetworkConfigurationPrivatePointer> &configurations)