[fix](test) Fix flaky assertion in test_streaming_insert_job_fetch_meta_error

[JNSimba]

What problem does this PR solve?

PR #62023 refactored the filesystem SPI, which changed the error propagation path in S3SourceOffsetProvider.fetchRemoteMeta().

Previously (#61284), the debug point created a GlobListResult with an error status, and the subsequent status check threw an exception with message "Failed to list S3 files: ...". After the refactoring in #62023, the debug point was changed to directly throw an IOException, which is caught by StreamingInsertJob.fetchMeta() and wrapped as "Failed to fetch meta, ...". However, the regression test assertion was not updated accordingly, causing the test to fail intermittently.

How does this PR fix it?

Update the assertion in test_streaming_insert_job_fetch_meta_error from checking "Failed to list S3 files" to "Failed to fetch meta", matching the actual error message produced by the current code path.

Release note

None

Check List (For Author)

• Test
  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a test fix — corrects the assertion string to match the actual error message.

Check List (For Reviewer who is not the Author)

• Confirm that the problem is correctly described and the solution makes sense
• Confirm that no Copyright information is lost
• Confirm that no sensitive data is included (such as S3 keys)

[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?

[JNSimba]

run buildall