[fix](build) Allow Doris hidden columns in Gitleaks

[hello-stephen]

Problem

Doris internal hidden column identifiers such as __DORIS_IVM_UNION_KEY_0_0_COL__ can match the generic-api-key heuristic even though they are deterministic schema names, not credentials.

Solution

Add a rule-scoped allowlist for the exact hidden-column pattern __DORIS_[A-Z0-9_]+_COL__.

Validation

• git diff --check
• Gitleaks 8.30.0 config parse and hidden-column sample scan: 0 findings
• PR [feature](ivm) Support incremental view maintenance (IVM) for materialized tables (MTMV) #62606 reproduction: generic-api-key false positive in the IvmNormalizeMTMVTest hidden-column assertion

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[hello-stephen]

skip buildall

[github-actions]

PR approved by anyone and no changes requested.

[github-actions]

PR approved by at least one committer and no changes requested.