[Feature] Allow copy_partitions when using microbatch

[borjavb]

resolves #
#1414

Problem

copy_partitions was only being allowed for insert_overwrite, but it makes sense to allowlist it when using microbatch too.

Solution

Allowlist copy_partitions as part of microbatch too.

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

[MichelleArk]

code-quality fix looks pretty small, and I believe the unit test issue may be resolved with a merge to main given we've done work on retries recently: 26c19e9

@borjavb - Let me know if you can make those changes in the next day or two as we're planning the 1.9 final release of dbt-bigquery on December 12 and this would be awesome to include! Otherwise I can take it over the finish line (credit will still go to you in the Changelog :))

Edit: totally my bad, I wrote December 12 when I meant December 9. We'll get this out in a 1.9 patch though!

[borjavb]

@MichelleArk Sorry, I was away from the computer for a few days! the code quality check should be fixed now 🙏 Added some extra tests to validate the set up too.