Stop trusting our old APT signing key

We started signing repositories with our new key, added via !682 (merged).

I'm not doing this for stable because this would require bumping APT snapshots, which requires more QA, and the old key expires on May 7 so this would only make a difference for the first few days of 4.30 lifetime.

I'm doing this for testing, even though that's mostly useless, to give us greater chances to spot trouble with this migration ASAP.

refs sysadmin#17810 (closed)

Edited by intrigeri

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