limit pip-tools version in testing-requirements
limit pip-tools version in testing-requirements

pip-tools 5.4 needs pip>=20.1, but we use 20.0.2. So, we need to lower
prevent installing a pip-tools 5.4+ to avoid accidentally updating pip.

Plexxi/st2,StackStorm/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,Plexxi/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2