QList benchmark: fix annoying -Wdeprecated-copy warning

MyPrimitive has a copy ctor but lacked a copy assignment operator,
leading to above-mentioned warning.

Fix by supplying the missing special member function.

Change-Id: Icd0c3c12554eb838b5d880ec9a649d0b5cfc81b7
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

tests/benchmarks/corelib/tools/qlist/main.cpp

@@ -103,6 +103,8 @@ struct MyPrimitive : public MyBase
     { ++errorCount; }
     MyPrimitive(const MyPrimitive &other) : MyBase(other)
     { ++errorCount; }
+    MyPrimitive &operator=(const MyPrimitive &other)
+    { ++errorCount; MyBase::operator=(other); return *this; }
     ~MyPrimitive()
     { ++errorCount; }
 };