fix unit tests related to new serialization api

[kwigley]

Description

This PR updates dbt-spark to use new serialization API that is the result of using Mashumaro in dbt-core. It also addresses failing unit tests as a result of updated the dbt-core version to 0.19.1b2

Checklist

• I have signed the CLA
• 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
• I have updated the CHANGELOG.md and added information about my change to the "dbt next" section.

[jtcohen6]

Nice one! I hope this wasn't too too tricky to debug.

Today, I guess it's fair game that breaking changes to dbt internals relevant to some adapter plugins can happen in patch releases, as long as it's not breaking for any end users. After v1.0, we should think about how plausible it is to keep plugin-facing changes within minor versions.

[gshank]

This looks good, but unfortunately the Mashumaro likely solution for handling omit_none columns is to go back to using 'omit_none', something which I'm going to switch to in dbt core this week. We might want to wait for a few days for that.

[kwigley]

@jtcohen6 100% agree, I'm interested in how we create and enforce this contract in core for different plugins. Will keep this in mind

[kwigley]

@gshank will the changes involve just renaming keep_none to omit_none? If so, I'm happy to merge this as is so we can release dbt-spark 0.19.1b2 and update the code with the mashumaro changes once they are merged. Let me know if that is not the case, I will hold off from merging

[kwigley]

Decided to merge this, I'm happy to update with any 0.19.1 changes