Move repo to the dependabot-fixtures org

[jeffwidman]

We should consider moving this repo into https://github.com/dependabot-fixtures

No rush on this, as there's a chance we may decide to go the other way and move the fixtures into this org and then tag the repos with something like test / fixtures for easy identification... (part of me actually leans that way for simplification--then everything public that's "dependabot-related" is in this org)

Mostly I'm opening this issue as a placeholder reminder that it's inconsistent that we have some test fixtures in this org and some in the other org. I'm not aware of any current guidelines that result in "smoke tests go this org, but other fixtures in the other org".

Also, we shouldn't move this repo until we've thought through how we want to handle the test-fixture-related repos in this org, such as https://github.com/dependabot/vgotest, https://github.com/dependabot/dummy-packages, https://github.com/dependabot/monolog etc