[roll third_party/pigweed] pw_presubmit: Fix git_repo.describe_files() output

- Use '@{upstream}' as the stand-in for the upstream tracking branch
  rather than an object.
- Make manually specifying @{u} or @{upstream} equivalent to the
  default behavior.
- Fix the git_repo.describe_files() output when comparing against
  @{upstream}.
- Move tracking branch handling into list_files() and describe_files()
  so it's consistent between pw format and pw presubmit.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/77540

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 2a0d4d58330bd4b..e586e3cca6bf505
Roller-URL: https://ci.chromium.org/b/8825655602563951441
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825655602563951441
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I0bb1e96c96b462aa17df9ed872a70c98e1d1fca4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/77542
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 2a0d4d5..e586e3c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2a0d4d58330bd4b2c120d2db8713b392e40cc342
+Subproject commit e586e3cca6bf5054a601e17136794dd14b0f9379