QArrayData: remove contradicting const qualifier from needsDetach()

The documentation above says it's intentionally not const and that's how
I had designed it. It was added by accident on with the noexcept
qualifier on commit c129362b4d ("Add a
couple of noexcept").

Change-Id: I8f3ce163ccc5408cac39fffd178c7fd237c6e079
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/tools/qarraydata.h

@@ -66,7 +66,7 @@ struct QArrayData
     // Returns true if a detach is necessary before modifying the data
     // This method is intentionally not const: if you want to know whether
     // detaching is necessary, you should be in a non-const function already
-    bool needsDetach() const noexcept
+    bool needsDetach() noexcept
     {
         return ref_.loadRelaxed() > 1;
     }