Test against matrix of dependencies

Problem statement

Pytester is intended as a library used by other projects. Therefore, we prefer to keep the dependency version constrain broad so that the projects have more room to choose the versions they desire. Currently we test pytester for differen python versions, but we do not test pytester for different dependency version:

Solution

Use tox to test pytester against a matrix of dependency versions. (Tox is a commonly used tool for this.) For starters, let's test against a matrix of the Databricks Python SDK as that is experimental. The lsql is a good second one as that is probably less stable than pytest itself. Finally we can test against different pytest versions, though, I assume that library to be quite stable, especially for the entrypoints we use (fixture)

https://github.com/databrickslabs/pytester/blob/979d22d334c4043f739371305e6b121c1a731eb1/pyproject.toml#L50-L54

Start by reading .github/workflows/push.yml around the existing Python-version matrix and pyproject.toml around the dependency constraints. Review the linked tox documentation, then define a tox-based matrix beginning with the Databricks Python SDK, followed by lsql and pytest versions. Done means CI tests pytester across the selected dependency versions.