Move media retention tests out of rest tests (#16684)

* Move media retention tests out of rest tests AFAICS this doesn't make any HTTP requests and so it ought not to belong in `tests.rest`. * Changelog
5 months ago · 0619c2bbd2
--- a/changelog.d/16684.misc
+++ b/changelog.d/16684.misc
@@ -0,0 +1 @@
 Reoranganise test files.
--- a/tests/rest/media/test_media_retention.py
+++ b/tests/rest/media/test_media_retention.py