[ci skip] Add 'LONGTEXT' to 'STRING' alias to CUBRID drivers for DBForge

Requested in #4640
diff --git a/system/database/drivers/cubrid/cubrid_forge.php b/system/database/drivers/cubrid/cubrid_forge.php
index 8262beb..46a3b21 100644
--- a/system/database/drivers/cubrid/cubrid_forge.php
+++ b/system/database/drivers/cubrid/cubrid_forge.php
@@ -178,6 +178,9 @@
 				$attributes['TYPE'] = 'INTEGER';
 				$attributes['UNSIGNED'] = FALSE;
 				return;
+			case 'LONGTEXT':
+				$attributes['TYPE'] = 'STRING';
+				return;
 			default: return;
 		}
 	}