Use pink for "Unbreak Now" priority instead of indigo

Summary:
Fixes T9237. A while ago, the old (more-pink) indigo got split into "pink" (more pink) and "indigo" (more purple), but we didn't change this color config in Maniphest.

This generally made the color more purple, and it's now pretty simliar to the "needs triage" color (violet).

Make it "pink" instead.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9237

Differential Revision: https://secure.phabricator.com/D13954