Pre-release version bump to 0.13.0 (#86)

* Bump version to `0.13.0`

* empty commit

---------

Co-authored-by: AndrewGardhouse <AndrewGardhouse@users.noreply.github.com>
Co-authored-by: Andrew Gardhouse <andrewgardhouse@gmail.com>

Author: github-actions[bot]

xanadu_sphinx_theme/_version.py

@@ -3,4 +3,4 @@
 using the following format: <major>.<minor>.<patch>[-<pre-release>].
 """
 
-__version__ = "0.13.0-dev"
+__version__ = "0.13.0"