Doc: Change the \section2 title to avoid wrong links

Change-Id: I4b6435f27d90d52a208b6fce8cc62a6868990a75
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>

doc/src/whatsnew/whatsnew50.qdoc

@@ -225,7 +225,7 @@
      \li New \l{AnimatedSprite} type for drawing single sprite animations.
     \endlist
 
-    \section2 Text
+    \section2 Changes to the Text types
     \list
      \li \l{Text}:
       \list