[Feature] Update release workflows to accept custom test command

### Is this your first time submitting a feature request?

- [X] I have read the [expectations for open source contributors](https://docs.getdbt.com/docs/contributing/oss-expectations)
- [X] I have searched the existing issues, and I could not find an existing issue for this feature
- [X] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

### Describe the feature

Currently release workflows assume that repos use Tox while testing ([example](https://github.com/dbt-labs/dbt-release/blob/640ebd8a9eae1a872ac06a7d263519714fff5c64/.github/workflows/build.yml)). Instead we want them to accept an optional argument, defaulting to `tox`, to allow packages to specify a custom test command.

### Describe alternatives you've considered

_No response_

### Who will this benefit?

_No response_

### Are you interested in contributing this feature?

_No response_

### Anything else?

_No response_