xml library tostring() accepts only one argument instead of 2

[Luis Sampaio]

Brief Description
-----------------
lxml library tostring() accepts only one argument instead of 2. This raises the following exception while trying to generate patches:

'tostring() takes exactly 1 positional argument (2 given)',)

Severity
--------
Low

Steps to Reproduce
------------------
Generate or modify a patch will throw the error

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/update/+/845013

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/update/+/845013
Committed: https://opendev.org/starlingx/update/commit/b94c464a7402e86d1dbaf970958b6ea3e4fa692e
Submitter: "Zuul (22348)"
Branch: master

commit b94c464a7402e86d1dbaf970958b6ea3e4fa692e
Author: Luis Sampaio <email address hidden>
Date: Tue Jun 7 09:20:24 2022 -0700

    Update tostring while writing xml

    lxml library tostring() accepts only one argument
    instead of 2 like it was before. This commit removes
    the second argument.

    Closes-Bug: 1977869

    Signed-off-by: Luis Sampaio <email address hidden>
    Change-Id: I9bb43a758bb660c8ab6edbf54984ff993b7f8598