[roll third_party/pigweed] pw_async_basic: Test flake fix

RunUntilIdle can execute tasks inline, which will mess up expected
order of test. Remove and just wait on last task to finish.

Original-Bug: b/323251704
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/189938

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 494b7f1305cde7c..0e8ccae17ac616b
Roller-URL: https://ci.chromium.org/b/8757330369121745985
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I9830cc6d7424bdf814e54488835063c6adaff7c1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/189939
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 494b7f1..0e8ccae 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 494b7f1305cde7c1215bbf178423c5f4153276ad
+Subproject commit 0e8ccae17ac616bcc325b59c7fda6970d3ac41e0