Probably fix bad URI construction for Diffusion symbols

Summary: Ref T9532.

Test Plan: I don't have this configured locally but this seems very likely to be the correct fix. This list should be a list of PHIDs, but is a list of PHIDs followed by one PhabricatorRepository object.

Reviewers: avivey, chad

Reviewed By: chad

Maniphest Tasks: T9532

Differential Revision: https://secure.phabricator.com/D14311