tst_QUrlQuery: fix Clang 15 -Wself-move

Says Clang 15:

  tst_qurlquery.cpp:193:11: warning: explicitly moving variable of type 'QUrlQuery' to itself [-Wself-move]
    moved = std::move(moved);
    ~~~~~ ^           ~~~~~

It's amazing how little it takes to throw this warning off guards:
just use an alising reference instead of the same variable. Makes you
wonder whether the time spent on detecting such trivialities in the
compiler is really well spent.

Amends fc8dad2f10.

Pick-to: 6.5
Task-number: QTBUG-109842
Change-Id: I165af2a786aa0ba28b8dcd039a500f3494bc29a9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/io/qurlquery/tst_qurlquery.cpp

@@ -190,11 +190,17 @@ void tst_QUrlQuery::constructing()
     QCOMPARE(moved, copy);
 
     // self move-assign
-    moved = std::move(moved);
+    {
+        auto &self = moved; // prevent -Wself-move
+        moved = std::move(self);
+    }
     QCOMPARE(moved, copy);
 
     // self move-assign of moved-from (Hinnant Criterion)
-    other = std::move(other);
+    {
+        auto &self = other; // prevent -Wself-move
+        other = std::move(self);
+    }
     // shouldn't crash; here, or further down
 
     // copy-assign to moved-from object