MySQL meta got "bad connection" error, should retry it

[anysql]

What would you like to be added:

2024/12/26 15:07:12.242607 juicefs[2716000] : error: bad connection

Check the shouldRetry function, if the database is postgresql it will retry, but not for mysql

    case "mysql":
            // MySQL, MariaDB or TiDB
            return strings.Contains(msg, "try restarting transaction") || strings.Contains(msg, "try again later") ||
                    strings.Contains(msg, "duplicate entry")
    case "postgres":
            return strings.Contains(msg, "current transaction is aborted") || strings.Contains(msg, "deadlock detected") ||
                    strings.Contains(msg, "duplicate key value") || strings.Contains(msg, "could not serialize access") ||
                    strings.Contains(msg, "bad connection") || errors.Is(err, io.EOF) // could not send data to client: No buffer space available

Why is this needed:

The bad connection error is reported by database/sql, when a connection lost abnormally, it's not a database specific error.
So mysql database should retry this error too.

[anysql]

Fixed in #5460