`wp_update_term()` should mimic `wp_insert_term()` and set a value for `$term_group` before the `alias_of` logic runs. This ensures that `$term_group` exists when `compact()` is called.

See [28461].
Fixes #29278.

Built from https://develop.svn.wordpress.org/trunk@29549


git-svn-id: http://core.svn.wordpress.org/trunk@29325 1a063a9b-81f0-0310-95a4-ce76da25c4cd