add script to override dev dependencies in tests

[emmyoop]

resolves dbt-labs/dbt-common#104

Problem

Sometimes we want to test dbt-core in CI against branches of dependencies.

Solution

Add a script to update the dependencies in dev-requirements.txt

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.

[emmyoop]

This was accidentally changed in a previous PR - this just adds it back

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.13%. Comparing base (0dc2a2f) to head (7092c37).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10023      +/-   ##
==========================================
- Coverage   88.19%   88.13%   -0.07%     
==========================================
  Files         181      181              
  Lines       22632    22632              
==========================================
- Hits        19961    19947      -14     
- Misses       2671     2685      +14     

Flag	Coverage Δ
integration	85.43% <ø> (-0.14%)	⬇️
unit	62.26% <ø> (ø)

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