[red-knot] Add 'mypy_primer' workflow (#16554)
## Summary
Run Red Knot on a small selection of ecosystem projects via a forked
version of `mypy_primer`.
Fork: https://github.com/astral-sh/mypy_primer
Branch: add-red-knot-support
## Test Plan
* Successful run:
https://github.com/astral-sh/ruff/actions/runs/13725319641/job/38390245552?pr=16554
* Intentially failed run where I commented out `unresolved-attribute`
diagnostics reporting:
https://github.com/astral-sh/ruff/actions/runs/13723777105/job/38385224144
