inference: type bound error due to free typevar in sparam env (#51013)
Fix #50709
This issue *appears* fixed on master due to #50432, which simply removed
the error. This fixes the underlying cause, which is that we sometimes
return typevars in the environment from intersection that have free vars
in their bounds. I think it's reasonable to just widen these
aggressively, since we usually cannot do much with these kinds of
unknown static parameters anyway.
(cherry picked from commit a3e23161b60e51d7aaa1183559dc70b9c28426e6)