Make 'tags' an error in runtests.py (GH-4772)
Make 'tags' an error in runtests.py (GH-4772)

We've now got rid of all legacy uses of "tags". Therefore make it an error instead of a warning to avoid new uses sneaking in.
scoder/cython,cython/cython,scoder/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,cython/cython,da-woods/cython,cython/cython,scoder/cython,da-woods/cython