savegame ex.: make Level ctor explicit

A QString is not a full representation of a Level, so the
Level(QString) ctor should be explicit.

Pick-to: 6.5 6.4 6.2 5.15
Task-number: QTBUG-108857
Change-Id: I24b705139e61c4aaf59cb0aad3b536013e0d07df
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

examples/corelib/serialization/savegame/level.h

@@ -14,7 +14,7 @@ class Level
 {
 public:
     Level() = default;
-    Level(const QString &name);
+    explicit Level(const QString &name);
 
     QString name() const;