Fix improper viewer for Git SSH cluster workflows
Summary: Ref T10751. These workflows have separate getUser() and getViewer() for weird legacy reasons. getUser() is correct.
- Did a Git SSH push, verified that "Last Writer" reflected the proper user in the "Storage" UI in repository management.
- Grepped for other callsites, double-checked that they used correct users.
Reviewed By: chad
Maniphest Tasks: T10751
Differential Revision: https://secure.phabricator.com/D15893