MDEV-34716 Fix mysql.servers socket max length too short

The limit of socket length on unix according to libc is 108, see
sockaddr_un::sun_path, but in the table it is a string of max length
64, which results in truncation of socket and failure to connect by
plugins using servers such as spider.

scripts/mysql_system_tables_fix.sql

@@ -851,3 +851,7 @@ DELIMITER ;
 ALTER TABLE servers
   MODIFY Host varchar(2048) NOT NULL DEFAULT '',
   MODIFY Owner varchar(512) NOT NULL DEFAULT '';
+
+# MDEV-34716 Fix mysql.servers socket max length too short
+ALTER TABLE servers
+  MODIFY Socket char(108) NOT NULL DEFAULT '';