Incremental models with a contract don't need their columns modified

[gshank]

resolves #10362

Problem

Incremental models with existing tables had their columns updated by "expand_target_column_types", but this is unnecessary when models have a contract.

Solution

Do not call "expand_target_column_types" when an incremental model has an enforced contract.

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/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

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.83%. Comparing base (25c2042) to head (abd2274).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10371   +/-   ##
=======================================
  Coverage   88.83%   88.83%           
=======================================
  Files         180      180           
  Lines       22704    22704           
=======================================
  Hits        20169    20169           
  Misses       2535     2535           

Flag	Coverage Δ
integration	86.06% <ø> (ø)
unit	62.24% <ø> (ø)

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Components	Coverage Δ
Unit Tests	62.24% <ø> (ø)
Integration Tests	86.06% <ø> (ø)

[mikealfare]

Approved, conditional on reverting the feature branch reference in dev-requirements.txt.

[mikealfare]

Reminder to revert this prior to merging.