workflow: run keywords check weekly (#22951)

[ti-chi-bot]

This is an automated cherry-pick of #22951

What is changed, added or deleted? (Required)

This PR changes the keywords check from a per-PR and push CI gate to a weekly, manually runnable, and repository-dispatch workflow.

After this change, the workflow:

• checks keywords.md on the configured branches, currently master and release-8.5;
• compares each docs branch with the TiDB parser branch of the same name;
• creates an issue only when keyword mismatches are found;
• skips parser download failures with a warning instead of reporting them as keyword mismatches;
• normalizes check-keywords.py to return 0 for success and 1 for any number of mismatches.

This reduces unnecessary disruption to unrelated PRs. Previously, every PR could be blocked by a keywords mismatch even when the PR did not touch keywords.md or parser-related content (see #22923 (comment)). With the new behavior, keyword drift is still monitored regularly, but it is reported as a maintenance issue instead of interrupting unrelated documentation changes.

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

@qiancai This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[gemini-code-assist]

Code Review

This pull request updates the scripts/check-keywords.py script to ensure that it exits with a standard status code of 1 if there are errors, or 0 if there are none, rather than exiting with the arbitrary count of errors. There are no review comments to address.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [qiancai]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment