roll: third_party/pigweed a9f2d91..d31705b (3 commits)

d31705b:https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/238533 pw_uart: Move non-blocking methods from Uart to UartBase
14204b5:https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/238532 pw_uart: Add uart_non_blocking_test to GN build
2a0f0df:https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/236723 pw_thread: Migrate from pw::thread::Thread to pw::Thread

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: a9f2d91c85fe01..d31705b84d24f0
Roller-URL: https://ci.chromium.org/b/8735614863452400737
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iaeac505f9d3a81883991205b84cf00af69737540
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/238348
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index a9f2d91..d31705b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a9f2d91c85fe017e27ec94b7502984818cc7c723
+Subproject commit d31705b84d24f0ef17e6b8eef6cae13f96f942e4