JNI: Don't use forwarding reference in ranged for

The elements we iterate over are always jobjects, i.e. POD, so iterating
over values is at least as efficient, and less unnecessarily clever.

Pick-to: 6.7
Change-Id: I6142dab84f3d37d82613ecf27cc03dde7810e541
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>

src/corelib/kernel/qjniarray.h

@@ -300,7 +300,7 @@ public:
         if constexpr (std::is_same_v<T, jobject>) {
             QList<jobject> res;
             res.reserve(size());
-            for (auto &&element : *this)
+            for (auto element : *this)
                 res.append(element);
             return res;
         } else if constexpr (std::is_same_v<T, jbyte>) {