Update test to handle moving from microbatch environment variable to behavior flag

[QMalcolm]

resolves #N/A

Problem

dbt-adapters and dbt-core are moving from using an environment variable for gating microbatch functionality to a behavior flag (dbt-labs/dbt-adapters#323, dbt-labs/dbt-core#10799). Additionally, dbt-adapters is adding more test stubs around this, and we wan to use those test stubs

Solution

Use the test stubs provided by dbt-adapters to test the switch from environment variable for gating microbatch functionality to a behavior flag.

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