[roll third_party/pigweed] pw_async2: Add PendableAsTask

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/201920

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 4c1a7158b663f11..bff185f46d3332f
Roller-URL: https://ci.chromium.org/b/8751181940596998993
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I0e171475d0e4085069b78c77b963e74771270e88
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/202630
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 4c1a715..bff185f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4c1a7158b663f114c297d9c0a806f412768e73f8
+Subproject commit bff185f46d3332f5bc89f74e33546ff689067920