SQL: avoid potential detach in QtSqlGlobals dtor

Wrap `connections` to std::as_const() to avoid unexpected detach
due to use of QHash::asKeyValueRange() in range-based for loop.

Change-Id: I2bf69782dc9dc63df0b3f9dfe395427909fba310
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/sql/kernel/qsqldatabase.cpp

@@ -122,7 +122,7 @@ QSqlDatabasePrivate::~QSqlDatabasePrivate()
 QtSqlGlobals::~QtSqlGlobals()
 {
     qDeleteAll(registeredDrivers);
-    for (const auto &[k, v] : connections.asKeyValueRange())
+    for (const auto &[k, v] : std::as_const(connections).asKeyValueRange())
         QSqlDatabasePrivate::invalidateDb(v, k, false);
 }