variable: allow setting system variable lc_messages

[djshow832]

What problem does this PR solve?

Issue Number: close #38231

Problem Summary:

#33708 breaks the compatibility of phpMyAdmin.

What is changed and how it works?

Set lc_messages back to not read-only.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Allow setting system variable `lc_messages`.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Defined2014
• morgo

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[wuhuizuo]

/run-mysql-test

[Defined2014]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 703670d

[Defined2014]

/hold

[Defined2014]

/cc @bb7133
PTAL

[Defined2014]

/unhold

[Defined2014]

/merge

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [1] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/common-test	🔴 failed 1, success 10, total 11	8 min 43 sec	Existing failure
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	29 min	Existing passed
idc-jenkins-ci/integration-cdc-test	🟢 all 37 tests passed	27 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	12 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 26 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	4 min 54 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	3 min 52 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	2 min 51 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 42 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed

[jaggerwang]

@djshow832 When this PR be merged to v6.1.x? I checked the latest v6.1.2's release notes, which released at 10/24, but it not contains this fix.

[jaggerwang]

@Defined2014

[Defined2014]

Not all bug fixes will be cherry-picked into LTS version. If you didn't found it by git log, the answer is no. Maybe you should wait v6.5.0 instead. :( @jaggerwang

[jaggerwang]

@Defined2014 As this error, we cannot use PHPMyAdmin to access TiDB.