QMetaObjectBuilder: fix \include snippet name

There's only qmetaenum-32bit-signextend-64bit, no
qmetaenum-32bit-zeroextend-64bit.

Fixes qdoc warning:

    Cannot find 'qmetaenum-32bit-zeroextend-64bit' in 'qmetaobject.cpp'

Amends f85a17a.

Task-number: QTBUG-111926
Change-Id: I5083d867e102fccbcd641fae5df3b47ba566a742
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qmetaobjectbuilder.cpp

@@ -2475,7 +2475,7 @@ int QMetaEnumBuilder::value(int index) const
     Returns the value with the given \a index if it exists; or returns a
     disengaged \c{std::optional} if it doesn't.
 
-    \include qmetaobject.cpp qmetaenum-32bit-zeroextend-64bit
+    \include qmetaobject.cpp qmetaenum-32bit-signextend-64bit
 
     \sa keyCount(), key(), addKey()
 */