Flake: TestSyncRegistry, TestNextSync and TestSyncerRun

Created by: indradhanush

• Name of tests: TestSyncRegistry, TestNextSync, TestSyncerRun
• Example failure: https://buildkite.com/sourcegraph/sourcegraph/builds/104488#0ffd8d62-3a23-4fb3-873e-659ab4fa6e72/341