I moved sourcecred/example-git{,hub} to the @sourcecred-test org.
This commit fixes the build given that move.
I've realized that in #1233 I in-advertently made some Git tests that
depend on a snapshot un-updateable. I'm going to compound on that slight
technical debt by skipping the tests that depended on that snapshot. I
recognize and accept that I'll need to pay this down when I resuscitate
the git plugin.
Test plan: `yarn test --full`.
