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

• [x] I have read the contributing guide and understand what's expected of me.
• [x] 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.
• [x] This PR includes type annotations for new and modified functions.

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[github-actions[bot]]

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[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 88.82%. Comparing base (300aa09) to head (478cd62). :warning: Report is 133 commits behind head on main.

:x: Your patch status has failed because the patch coverage (20.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

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%)	:arrow_down:
unit	62.81% <20.00%> (-0.01%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

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

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[colin-rogers-dbt]

supplanted by #11614