v4.20.0-rc1 will be replaced shortly

Stream: nightly-testing

[Kim Morrison]

I've already bumped a few repositories up to v4.20.0-rc1, but we've discovered a problem and will release v4.20.0-rc2 shortly, and then move everything up to that.

No action required by anyone, I just want to save anyone the effort of moving anything to rc1 in the meantime.