Update hook docs in wp-admin/edit-tag-form.php to use `WP_Term` instead of generic `object` type

[ocean90]

wp-admin/edit-tag-form.php still uses object for all $tag parameters although we now have a specific WP_Term object, see [34997].

https://core.trac.wordpress.org/browser/tags/4.9.4/src/wp-admin/term.php?marks=23,67#L21

[xhezairi]

Update hook docs to use WP_Term instead of object.

[SergeyBiryukov]

In 42822:

Docs: Use WP_Term instead of generic object type for the $tag parameter in wp-admin/edit-tag-form.php hook docs.

Props xhezairi, ocean90.
Fixes #43507.