Bors gets confused if a repo is transfered to another org

[dpp23]

When you transfer a Github repository to another org, bors seem to get stuck.

We did this with one of our private repositories against our own bors instance. What happened was that bors was still showing the repo from the old org.

When we tried to authorize the app with the repo in the new org, we got:

09:27:31.213 pid=<0.11885.94> [error] Task #PID<0.11885.94> started from #PID<0.11884.94> terminating
** (Ecto.ConstraintError) constraint error when attempting to insert struct:

    * unique: projects_repo_xref_index

If you would like to convert this constraint into an error, please
call unique_constraint/3 in your changeset and define the proper
constraint name. The changeset has not defined any constraint.

    (ecto) lib/ecto/repo/schema.ex:574: anonymous fn/4 in Ecto.Repo.Schema.constraints_to_errors/3
    (elixir) lib/enum.ex:1314: Enum."-map/2-lists^map/1-0-"/2
    (ecto) lib/ecto/repo/schema.ex:559: Ecto.Repo.Schema.constraints_to_errors/3
    (ecto) lib/ecto/repo/schema.ex:222: anonymous fn/14 in Ecto.Repo.Schema.do_insert/4
    (ecto) lib/ecto/repo/schema.ex:774: anonymous fn/3 in Ecto.Repo.Schema.wrap_in_transaction/6
    (ecto) lib/ecto/adapters/sql.ex:576: anonymous fn/3 in Ecto.Adapters.SQL.do_transaction/3
    (db_connection) lib/db_connection.ex:1283: DBConnection.transaction_run/4
    (db_connection) lib/db_connection.ex:1207: DBConnection.run_begin/3
Function: #Function<5.18273092/0 in BorsNG.Worker.SyncerInstallation.start_synchronize_installation/1>
    Args: []

We resolved it by nuking the bors database in our instance, but if someone transfers a public repository connected to the public bors they will probably get stuck.