Trouble showing showing Posts related to custom post type and taxonomy.

Try this:

$the_query = new WP_Query($args = array(
      'post_type' => 'forms',
      'tax_query' => array(
        array(
            'taxonomy' => 'form_category',
            'field'    => 'slug'
        ),
      ),

    )
);

btw – Why do you have a 0 in this add_action? Remove it or change it to > 0.

add_action( 'init', 'my_taxonomies_product', 0 );