Backport PR #34711 on branch 1.0.x (BLD: Pin cython for 37-locale build)
xref #34711
see https://github.com/pandas-dev/pandas/pull/34711#issuecomment-644148383, abort this backport? closing for now. I probably should have pinned at 0.29.13 anyway. cc @jorisvandenbossche just to be aware i've closed this. OK!