bpo-36407: Fix writing indentations of CDATA section (xml.dom.minidom). (GH-12514)

diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 43569dd..464420b 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -862,7 +862,8 @@
         if self.childNodes:
             writer.write(">")
             if (len(self.childNodes) == 1 and
-                self.childNodes[0].nodeType == Node.TEXT_NODE):
+                self.childNodes[0].nodeType in (
+                        Node.TEXT_NODE, Node.CDATA_SECTION_NODE)):
                 self.childNodes[0].writexml(writer, '', '', '')
             else:
                 writer.write(newl)