Switch from "master" to "main"

This really only affects builders that don't specify the branch but as
of pwirev/12060 those no longer exist. It affects many recipe tests as
well.

Bug: 209
Change-Id: I879a77bdac3f8ca66fefdc2119d53bd9128df4c1
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/43462
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Marc-Antoine Ruel <maruel@google.com>
105 files changed