[test-suite] Set up .arcconfig to point to new Diffusion T repository
We want to automatically copy the appropriate mailing list
for review requests to the test-suite repository.
For context, see the proposal and discussion here:
Similar to D40179, I set up a new Diffusion repository with callsign
"T" for test-suite:
This explicitly updates test-suite's .arcconfig to point to the new
T repository in Diffusion, which will let us use Herald rule H270.
Reviewers: klimek, sammccall
Reviewed By: sammccall
Subscribers: llvm-commits, dlj, bkramer
Differential Revision: https://reviews.llvm.org/D40502