[fix](statistics) Fix missing Mockito import in AnalysisManagerTest

[yujun777]

What problem does this PR solve?

Issue Number: N/A

Related PR: #62710

Problem Summary: AnalysisManagerTest in the adaptive_batch_size branch is missing the import org.mockito.Mockito; statement needed by the Mockito-based test methods introduced in #62686/#62710. Without this import the FE build fails at compilation with cannot find symbol: variable Mockito.

Release note

None

Check List (For Author)

• Test: No need to test (compile fix only, import statement only)
• Behavior changed: No
• Does this need documentation: No

[hello-stephen]

Thank you for your contribution to Apache Doris.
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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?

[yujun777]

run buildall

[yujun777]

/review

[github-actions]

No blocking findings.

Review conclusion: approve.

Critical checkpoints:

• Goal of the current task: Met. The PR adds the missing org.mockito.Mockito import required by existing Mockito calls in AnalysisManagerTest at the PR head. The base commit already contains those Mockito.* usages without the import, so this is a real compile-fix.
• Minimality and focus: Met. This is a single-file, one-line, test-only change and is as small as possible.
• Concurrency: Not applicable. No concurrent or lock-sensitive runtime code is changed.
• Lifecycle and static initialization: Not applicable. No lifecycle or static initialization logic is touched.
• Configuration changes: Not applicable. No config is added or modified.
• Compatibility and incompatible changes: Not applicable. No FE-BE protocol, API surface, symbol, or storage-format change is involved.
• Functionally parallel code paths: Not applicable. This patch only fixes the test import in the affected file.
• Special conditional checks: Not applicable. No new conditional logic is introduced.
• Test coverage: Acceptable for a compile-fix. The existing Mockito-based tests are already present in this file; this import is what allows them to compile. I could not run the prescribed FE build or test flow locally because thirdparty/installed/bin/protoc is missing in this runner, which blocks the fe/AGENTS.md build prerequisites.
• Observability: Not applicable. No runtime behavior changes.
• Transaction and persistence: Not applicable. Not involved.
• Data writes and modifications: Not applicable. Not involved.
• FE-BE variable passing: Not applicable. Not involved.
• Performance: No impact.
• Other issues: None found in the PR diff.

Based on the patch scope and the evidence above, I do not see any blocking issue in this PR.