doc: Fix QString::slice() code example

The snippet referred to had a duplicate identifier to an earlier snippet
in the snippet file, causing that one to be quoted instead.

Change-Id: Id46f6da807806f874291cd5d4c25b8884e511cfc
Reviewed-by: Nicholas Bennett <nicholas.bennett@qt.io>
(cherry picked from commit d2c9982a568181d55a9043c8646a4ee88b635fc7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/doc/snippets/qstring/main.cpp

@@ -912,11 +912,11 @@ void Widget::arrayOperator()
 
 void Widget::sliceFunction()
 {
-    //! [97]
+    //! [slice97]
     QString x = u"Nine pineapples"_s;
     x.slice(5);     // x == "pineapples"
     x.slice(4, 3);  // x == "app"
-    //! [97]
+    //! [slice97]
 }
 
 

src/corelib/text/qstring.cpp

@@ -5430,7 +5430,7 @@ QString QString::sliced_helper(QString &str, qsizetype pos, qsizetype n)
     \note The behavior is undefined if \a pos < 0, \a n < 0,
     or \a pos + \a n > size().
 
-    \snippet qstring/main.cpp 97
+    \snippet qstring/main.cpp slice97
 
     \sa sliced(), first(), last(), chopped(), chop(), truncate()
 */