dm failed to run when only ssl-ca is configured

[D3Hunter]

What did you do?

• target db is tidbcloud tidb cluster
• use ssl to connect target db, tidbcloud only has ca part
• start-task, and fail with "Message": "[Lightning:DB:ErrDBConnect]failed to connect database: could not load client key pair: tls: failed to find any PEM data in certificate input",

bug was introduced in #3260, if user didn't specify some ssl-xxx(like in here, there's only ssl-ca config, no ssl-cert and ssl-key), we should not dump it.

tiflow/dm/config/security/security.go

Lines 105 to 109 in 45ee743

	if isSSLCertNotExist {
	s.SSLCert = path.Join(baseDirPath, "cert.pem")
	if err := utils.WriteFileAtomic(s.SSLCert, s.SSLCertBytes, 0o600); err != nil {
	return err
	}

task cfg

name: test
task-mode: all

target-database:
  host: "xxxxxx.clusters.dev.tidb-cloud.com"
  port: 4000
  user: "root"
  password: "xxx"
  security:
    ssl-ca: "tidbcloud-ca.pem"

mysql-instances:
  - source-id: "mysql-3306"
    block-allow-list: "ba-rule1"
    syncer-config-name: "global"

block-allow-list:
  ba-rule1:
    do-dbs: ["test"]

syncers:
  global:
    worker-count: 1
    batch: 1

What did you expect to see?

success

What did you see instead?

fail

Versions of the cluster

tested using 6.1.3, but is should fail on current master too, master branch change lightning tls config to sslCABytes, so no such problem

current status of DM cluster (execute query-status <task-name> in dmctl)

(paste current status of DM cluster here)