Set up testing between branches of dbt-core and dbt-common

[emmyoop]

Description

We need to be confident that changes to dbt-common don't break dbt-core and adapter. This ticket is only scoped to the relationship between dbt-core and dbt-common.

Acceptance Criteria

1. Be able to run integration tests in dbt-core by pointing to a branch of dbt-common
2. Before merging PRs in dbt-common validate it works by running all tests for dbt-core with the merged version of dbt-common changes. If the tests fail, do no merge the PR. This prevents us from having to run the tests constantly for every commit in dbt-common, slowing down development. We can manually run them anytime using the first scenario if we think there's a high chance of breaking core. But this safeguards merges that definitely break core. One option to do this is to use merge queues. This will trigger the workflows to run once added to the merge group (when dev hits merge) but if CI fails it will get pulled out of the queue and not actually merged.

Impact to Other Teams

None

Suggested Testing

N/A - CI work

Context

Example of how dbt-snowflake tests against branches of dbt-core

Suggested approach:

1. check out dbt-core off a configurable branch (main by default)
2. install dbt-core dependencies
3. install the current branch of dbt-common to overwrite the defined dependency
4. run tests (integration + unit)