QA: Disable known-failing test on CI targets

Don't run the "Canceling reply leaves usable form" test in our CI jobs
on en.wikipedia.beta.wmflabs.org and test2.wikipedia.org.

(Change Iffaebf86b9c243 tried @wip but that doesn't work, see zfilipin
comment. It's still a useful annotation.)

Change-Id: Ice6fb4a7c2fc0f8fca9d328397b839db9cae92bf
Merge "QA: Disable known-failing test on CI targets"