[Cython] Cython 3.0 RC 2 released

Hi all, after close to five long years, we're almost there – I've pushed a release candidate for Cython 3.0 with a long list of bug fixes (followed by a second one with one important fix). https://cython.readthedocs.io/en/latest/src/changes.html Please give it some final testing. Unless we find something really serious in the RC2 release, the changes for the final release will be very limited and safe, hopefully none at all. The RC is just in time for this week's US-SciPy, and I'll make sure we have a final release for next week's EuroPython in Praha. Have fun, Stefan