Docs: Add a @since note to get_the_archive_title() about the title part being wrapped in a <span> element.

Follow-up to [48294].

Props justinahinon, audrasjb.
Merges [48814] to the 5.5 branch.
Fixes #51050.

git-svn-id: https://develop.svn.wordpress.org/branches/5.5@48815 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/general-template.php

@@ -1645,6 +1645,7 @@ function the_archive_title( $before = '', $after = '' ) {
  * Retrieve the archive title based on the queried object.
  *
  * @since 4.1.0
+ * @since 5.5.0 The title part is wrapped in a `<span>` element.
  *
  * @return string Archive title.
  */