patch for bigquery unittest with sql_header

[Kayrnt]

Resolves #9775
Based of @takemikami post on fixing SQL header integration in unit tests for BigQuery.

Problem

Solution

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.

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[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.82%. Comparing base (300aa09) to head (478cd62).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11386      +/-   ##
==========================================
- Coverage   88.90%   88.82%   -0.08%     
==========================================
  Files         191      191              
  Lines       24391    24394       +3     
==========================================
- Hits        21684    21669      -15     
- Misses       2707     2725      +18     

Flag	Coverage Δ
integration	85.77% <100.00%> (-0.15%)	⬇️
unit	62.81% <20.00%> (-0.01%)	⬇️

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Components	Coverage Δ
Unit Tests	62.81% <20.00%> (-0.01%)	⬇️
Integration Tests	85.77% <100.00%> (-0.15%)	⬇️

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