torproject time-based snapshots for stretch pull from buster

Originally created by @anonym on #13413 (Redmine)

While working on tails/tails#13253 I first tried to be efficient by just bumping the torprojet snapshot to pull the new Tor 0.3.0.9. Specifically we expect to get 0.3.0.9-1~d90.stretch+1 but we get 0.3.0.9-1~d99.buster+1 (also affects devel.

Our APT pinnings look good; actually it seems the time-based snapshot is wrong, cause the 2017070402 torproject snapshot for stretch has version 0.3.0.9-1~d99.buster+1, which seems wrong.

Starting with an elevated priority since if this affects e.g. the debian snapshots this probably could be serious.

Related issues

• Blocks tails/sysadmin#13233
• Blocks tails/tails#13416