Pin setuptools to address setuptools#4483

[mikealfare]

Problem

setuptools released 71.0.0 and 71.0.1 last night which contains a breaking change. This is blocking our CI. See pypa/setuptools#4483 for more information.

Solution

• create a separate build-requirements.txt file to isolate build dependencies
• pin setuptools~=70.0 in this file
• reference this file in dev-requirements.txt for backwards compatibility
• install from this file in workflows instead of running pip install --upgrade setuptools ...

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

[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 dbt-bigquery contributing guide.

[mikealfare]

We were installing this directly and upgrading, so we never actually used 4.0. 4.0 is also broken, see pypa/twine#977. From the post in there, the date of the fix, and the dates of the releases, the fix was released as part of 5.0.

[mikealfare]

We don't actually need this.