Require ply version to be less than 3.10
Require ply version to be less than 3.10

We have observed an issue with this version of ply, with the ELSE token
not being parsed correctly in P4 programs. I am unsure whether this is
an issue with ply or the p4-hlir code. The best fix right now seems to
require an older version of ply.

p4lang/p4-hlir