Fix typo in xml.dom.minidom documentation (GH-10956)

Escape the \t and \n.
Follow up from https://github.com/python/cpython/pull/10814.
(cherry picked from commit 2d8f976c)
Co-authored-by: E Kawashima <e-kwsm@users.noreply.github.com>

Doc/library/xml.dom.minidom.rst

@@ -169,7 +169,7 @@ module documentation.  This section lists the differences between the API and
       the *encoding* argument was introduced; see :meth:`writexml`.
 
 
-.. method:: Node.toprettyxml(indent="\t", newl="\n", encoding=None)
+.. method:: Node.toprettyxml(indent="\\t", newl="\\n", encoding=None)
 
    Return a pretty-printed version of the document. *indent* specifies the
    indentation string and defaults to a tabulator; *newl* specifies the string