Dev channel update to 86.0.615.3 is live

MatureScarab582 since vertical tabs hasn't been enabled in code yet, the only way to get it is via our experimentation platform.  Unfortunately, one of the drawbacks of that is that every time Edge updates, it reassesses the probability for whether or not to enable the feature, assuming that it's not turned on for 100% of people.  Once it's turned on in code, which means everybody will get it, I'll mention it in the release notes.