fix: Address warnings with QSet::fromList in Qt 5.15

Starting with Qt 5.15, the conversion functions between QList and QSet
(e.g., `QSet::fromList`) have been deprecated in favor of range constructors.

This change updates the code to use the new range constructors to avoid
deprecation warnings starting from Qt 5.14 (instead of Qt 6)

Related upstream Qt commits:
* qt/qtbase@92f984273 ("Deprecate conversion functions between QList and QSet", 2019-05-07)
* qt/qtbase@e59e5643b ("Use QT_DEPRECATED_X instead of Q_DECL_DEPRECATED_X", 2020-02-25)

(cherry picked from commit commontk/PythonQt@630e376)

Author: jcfr

src/PythonQtClassInfo.cpp

@@ -562,7 +562,7 @@ QStringList PythonQtClassInfo::memberList()
     }
   }
 
-#if QT_VERSION >= 0x060000
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
   QSet<QString> set(l.begin(), l.end());
   return set.values();
 #else

src/PythonQtClassWrapper.cpp

@@ -477,7 +477,7 @@ static PyObject *PythonQtClassWrapper_getattro(PyObject *obj, PyObject *name)
 
     auto members = wrapper->classInfo()->memberList();
     auto properties = wrapper->classInfo()->propertyList();
-#if QT_VERSION >= 0x060000
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
     QSet<QString> completeSet(members.begin(), members.end());
     completeSet.unite(QSet<QString>(properties.begin(), properties.end()));
 #else