validate_document & add_auto_capture_dropdown should be static

[VictorMinemu]

No description provided.

[VictorMinemu]

These two methods are called statically. In a production environment, it makes PHP fail making the order page crash.
Here is an example debug log:

[13-Nov-2021 23:46:06 UTC] PHP Fatal error:  Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method EBANX\Plugin\Services\WC_EBANX_Capture_Payment::add_auto_capture_dropdown() cannot be called statically in /homepages/31/d802735309/htdocs/..../wp-includes/class-wp-hook.php:303
Stack trace:
#0 /homepages/31/d802735309/htdocs/..../wp-includes/plugin.php(189): WP_Hook->apply_filters(Array, Array)
#1 /homepages/31/d802735309/htdocs/..../wp-content/plugins/woocommerce/includes/admin/meta-boxes/class-wc-meta-box-order-actions.php(40): apply_filters('woocommerce_ord...', Array)
#2 /homepages/31/d802735309/htdocs/..../wp-admin/includes/template.php(1395): WC_Meta_Box_Order_Actions::output(Object(WP_Post), Array)
#3 /homepages/31/d802735309/htdocs/..../wp-admin/edit-form-advanced.php(681): do_meta_boxes(Object(WP_Screen), 'side', Object(WP_Post))
#4 /homepages/31/d802735309/htdocs/..../wp-admin/post.php(206): require('/homepages/31/d...')
#5 {main}
  thrown in /homepages/31/d802735309/htdocs/..../wp-includes/class-wp-hook.php on line 303