Alphabetical order in taxonomy.php

The main query is generated before the template is loaded, the results of the main query are how WordPress knows what template to load. If you want to alter query parameters of the main query to change things like orderby, you should add a function hooked to pre_get_posts.

The argument passed to the function contains the query parameters of each query, so you can check which query it is and only alter your taxonomy main query. This function would go in your theme’s functions.php file, or a plugin.

function wpd_adhesion_taxonomy_queries( $query ) {
    if ( !is_admin() && $query->is_tax( 'adhesion' ) && $query->is_main_query() ) {
        $query->set( 'orderby', 'title' );
        $query->set( 'order', 'ASC' );
    }
}
add_action( 'pre_get_posts', 'wpd_adhesion_taxonomy_queries' );