Use job dependency flow for CI jobs

The Ruby SDK cleaned up their CI flow by using job dependency flows:

@neel.shah said:

> btw probably interesting for everyone, @peter made the ruby CI really clean by creating a job dependency flow
> it looks like this
>
> [https://github.com/getsentry/sentry-ruby/actions/runs/15043844757](https://github.com/getsentry/sentry-ruby/actions/runs/15043844757)
> the main file is this
> [https://github.com/getsentry/sentry-ruby/blob/master/.github/workflows/tests.yml](https://github.com/getsentry/sentry-ruby/blob/master/.github/workflows/tests.yml)
> that invokes each specific test matrix
> [https://github.com/getsentry/sentry-ruby/blob/master/.github/workflows/sentry_ruby_test.yml](https://github.com/getsentry/sentry-ruby/blob/master/.github/workflows/sentry_ruby_test.yml)

We could implement something similar for the Python SDK to better group tests. We already have some grouping, but this grouping basically puts all tests for different categories in different jobs. Instead, we could have a single job for tests, with all the current groups as sub-jobs of that main test job