Tests: Add unit tests for wp_ajax_inline_save_tax()

[pbearne]

This PR adds unit tests for the wp_ajax_inline_save_tax() function located in src/wp-admin/includes/ajax-actions.php.

The tests cover:

• Successful update of a term via Quick Edit.
• Proper handling of invalid nonces (taxinlineeditnonce).
• Validation of the taxonomy parameter.
• Behavior when the tax_ID parameter is missing.
• Verification of user permissions (edit_term capability).

Trac ticket: https://core.trac.wordpress.org/ticket/65252

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