During the initial migration from Sauce Labs to AWS Device Farm, we added the @device_farm tag to a few ui tests. Now that our ui tests have stabilized a bit, I'd like to try re-enabling these two, which are currently skipped in every configuration that we ever run in DTT or drone. For a cheat sheet on what runs where, see: https://github.com/code-dot-org/code-dot-org/blob/staging/dashboard/test/ui/README.md#cicd-testing

Testing story

• both re-enabled tests had at least 5 passing runs in drone
• mix_move_ai.feature ui test consistently failed in chromedriver, then passed on the first retry in Device Farm (we allow up to 2 retries). this pattern is not currently considered to be a blocking issue, and there are ~10 other tests which behave similarly.
• teacher_student_toggle.feature eyes test passed 5x on the first run against local chromedriver. for good measure, I ran an additional drone run with [skip local webdriver] to force it to run in Device Farm, which is where it will run during the DTT.

Deployment notes

• expect some eyes diffs in teacher_student_toggle.feature, as this eyes test has been disabled during the DTT for some weeks since we cut over eyes tests from sauce to device farm.

Follow-up work

• if either of these turn out to be flaky during DTT or drone, we can consider disabling them again. if we do, we should consider using the @skip to make it clearer that these tests are being skipped in all current run configurations, rather than silently using a combination of tags that effectively skips the feature.
• re-enabling Mix Move AI helps unblock the effort to move ui tests off of prod courses, without silently breaking the test.