You can stop the Schema Change along with Direct Query and No Caching warnings in these two ways-
global $wpdb;
$wpdb->query( "DROP TABLE IF EXISTS {$wpdb->prefix}rest_of_the_name" ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.NoCaching, WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.SchemaChange
or
global $wpdb;
// @codingStandardsIgnoreStart
$wpdb->query( "DROP TABLE IF EXISTS {$wpdb->prefix}rest_of_the_name" );
// @codingStandardsIgnoreEnd