Not providing optional `$taxonomy` parameter in `get_edit_term_link()` leads to incorrect URL

[flixos90]

In #35922, the $taxonomy parameter of get_edit_term_link() was made optional, as part of a greater effort to automatically determine the correct taxonomy for the given term. See also [36646] and follow-up [36986].

However, with that function it appears there was an oversight in that change, as the not providing the parameter leads to an incorrect URL returned: While in one place the function gets the taxonomy from the term object in a $tax variable, in another place the function still uses the originally passed $taxonomy parameter, which leads to this bug.

Despite being present for many years now, this bug probably hasn't been spotted because get_edit_term_link() isn't used much directly, as the edit_term_link() function is usually used. Since the function still passes the correct $taxonomy parameter to get_edit_term_link(), there's no problem in that situation. But calling get_edit_term_link() without a $taxonomy parameter leads to the incorrect URL.

To illustrate the bug with an example:

• Let's say there's a category with ID 42.
• Call get_edit_term_link( 42 ).
• The result will be https://example.org/wp-admin/term.php?tag_ID=42&post_type=post. But it should be https://example.org/wp-admin/term.php?taxonomy=category&tag_ID=42&post_type=post.
• Accessing the incorrect URL will in most scenarios lead to an error screen, because the taxonomy query parameter is missing.

The fix should be rather straightforward: Instead of using $taxonomy to populate the taxonomy query parameter, we need to use $tax, which always contains the correct taxonomy.

A test should also be added to verify the bug is fixed.

[flixos90]

cc @boonebgorges for visibility

Trac Ticket: Core-61726

## Problem

• The get_edit_term_link() function currently generates an incorrect URL when the $taxonomy parameter is omitted. This issue arises because $taxonomy was made optional, aiming to automatically determine the correct taxonomy from the term object ($tax). However, the implementation overlooked consistently using $tax->name to populate the taxonomy query parameter in all scenarios.

## Solution

• To resolve this issue, we have updated get_edit_term_link() to consistently use $tax->name instead of $taxonomy when generating the URL. This ensures that the correct taxonomy name is always included in the URL structure, preventing errors and inconsistencies.

## Steps to Reproduce

• Call get_edit_term_link( 42 ) where 42 is the ID of a term.

-Without the fix, observe that the generated URL lacks the taxonomy parameter, leading to incorrect behavior.

## Changes Made

• Modified get_edit_term_link() to use $tax->name for populating the taxonomy query parameter.

## Testing

• Tested the fix by invoking get_edit_term_link() with and without the $taxonomy parameter.
• Verified that the URL structure is correct in both cases and no errors occur.
• This enhancement ensures consistent behavior in get_edit_term_link() when determining the correct taxonomy for generating term edit URLs.

Hi @felixarntz , Thanks you for the feedback, I have addressed them and made the necessary changes, assigning you again for re-review.

[flixos90]

In 58807:

Taxonomy: Ensure get_edit_term_link() produces the correct result when called without taxonomy.

This fixes an oversight missed in [36646].

Props debarghyabanerjee.
Fixes #61726.
See #35922.

Committed in https://core.trac.wordpress.org/changeset/58807