Doc/library/xml.etree.elementtree.rst: Use ".. note::" for backport notes

.. to make it consistent with Doc/library/pyexpat.rst.

Author: hartwork

Doc/library/xml.etree.elementtree.rst

@@ -1398,7 +1398,9 @@ XMLParser Objects
       Disabling reparse deferral has security consequences; please see
       :meth:`xml.parsers.expat.xmlparser.SetReparseDeferralEnabled` for details.
 
-      Note that :meth:`flush` has been backported to some prior releases of
+      .. note::
+
+      :meth:`flush` has been backported to some prior releases of
       CPython as a security fix.  Check for availability of :meth:`flush`
       using :func:`hasattr` if used in code running across a variety of Python
       versions.
@@ -1476,7 +1478,9 @@ XMLPullParser Objects
       Disabling reparse deferral has security consequences; please see
       :meth:`xml.parsers.expat.xmlparser.SetReparseDeferralEnabled` for details.
 
-      Note that :meth:`flush` has been backported to some prior releases of
+      .. note::
+
+      :meth:`flush` has been backported to some prior releases of
       CPython as a security fix.  Check for availability of :meth:`flush`
       using :func:`hasattr` if used in code running across a variety of Python
       versions.