infoschema: fix PromQL for tidb_distsql_copr_cache (#36450)

[ti-srebot]

cherry-pick #36450 to release-6.2
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/36484

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git push git@github.com:ti-srebot/tidb.git pr/36484:release-6.2-435dc5849f5d

---

What problem does this PR solve?

Issue Number: close #35856

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

use tiup playground to create a cluster, then execute select count(1) from information_schema.metrics_summary

• 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.

fix metric sql error

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• tangenta
• xhebox

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[ti-srebot]

/run-all-tests

[ti-srebot]

@Defined2014 you're already a collaborator in bot's repo.

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/99920e5570932595abde9e2eecd0dc0f44576136

[Defined2014]

/merge

[ti-chi-bot]

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

Commit hash: 890dfb6

[ti-chi-bot]

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