feat(tidb): update go image

[purelind]

use the go1.21 image in mysql-test.

[ti-chi-bot]

I have already done a preliminary review for you, and I hope to help you do a better job.
Based on the pull request description and the diff, the key change is updating the golang image used in the pod-ghpr_mysql_test.yaml file from "hub.pingcap.net/jenkins/centos7_golang-1.20:latest" to "hub.pingcap.net/wangweizhen/tidb_image:go12120230809".

Potential problems:

• It's not clear why the image needed to be updated. If this information is important, it should be added to the pull request description or commit message.
• The new image may not work as expected. It's possible that the new image may have some compatibility issues with the existing codebase, which may cause the tests to fail or produce unexpected results.

Fixing suggestions:

• Add a brief explanation in the pull request description or commit message about why the image needed to be updated.
• Before merging the pull request, run the test suite with the new image to ensure that everything is still working as expected. If there are any issues, they should be addressed before merging the pull request.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wuhuizuo

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• pipelines/OWNERS [wuhuizuo]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-09 07:40:49.288780714 +0000 UTC m=+98413.837796701: ☑️ agreed by wuhuizuo.