metrics: fix wrong bucket name of coprocessor cache (#22454)

[ti-srebot]

cherry-pick #22454 to release-4.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/22617

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/22617:release-4.0-94fe8d954e6e

---

Signed-off-by: lzmhhh123 lzmhhh123@gmail.com

What problem does this PR solve?

Problem Summary:

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Side effects

• None

Release note

• fix wrong bucket name of coprocessor cache.

[ti-srebot]

/run-all-tests

[ti-srebot]

@lzmhhh123 you're already a collaborator in bot's repo.

[wshwsh12]

LGTM

[XuHuaiyu]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu

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[zhouqiang-cl]

/merge

[ti-chi-bot]

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

Commit hash: 719fcdf

[ti-chi-bot]

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