CI: blacklist problematic pytest-xdist versions
CI: blacklist problematic pytest-xdist versions

spacetelescope/asv,spacetelescope/asv,qwhelan/asv,airspeed-velocity/asv,airspeed-velocity/asv,qwhelan/asv,qwhelan/asv,spacetelescope/asv,airspeed-velocity/asv,qwhelan/asv,airspeed-velocity/asv,spacetelescope/asv