chore: run all tests by default

What does this merge request do and why?

In !503 (comment 1703597862), we found that:

This is very surprising that we have not tested in the some folders e.g. tests/instrumentators/test_model_requests.py.

We should always run all of the test cases under the tests folder.

e.g. https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/jobs/5799860235 should have failed but it passed.

We should ensure that all tests under tests folder run always.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.