Prefix secrets with DBT_ENV_SECRET_ for test env vars

[mikealfare]

resolves dbt-labs/adapters-team-private#133

Problem

Environment variables containing secrets need to be prefixed with DBT_ENV_SECRET_ to be handled properly in dbt-core.

Solution

• prefix testing environment variables with DBT_ENV_SECRET_
• update the places where they get read in in /tests
• update workflows that inject secrets
• update tox.ini
• update the oauth token refresh process

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-snowflake contributing guide.

[mikealfare]

A single instance of a test failed, it does not look like the secrets broke anything: https://github.com/dbt-labs/dbt-snowflake/actions/runs/8838621363/job/24270205847

[mikealfare]

New CI run: https://github.com/dbt-labs/dbt-snowflake/actions/runs/8853470288