[roll third_party/pigweed] pw_chrono/system_timer: Update destructor contract

Updates the pw::chrono::SystemTimer destructor contract to
explicitly state (and require) that the destructor block if
necessary until the expiry callback is no longer and can no longer
be executed.

This ensures SystemTimers can be safely used as members in objects
which are destructed.

Note that this is already met by the upstream backends including
FreeRTOS, STL, embOS, and Zephyr.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/75280

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: b8f3ad2db9ad0f0..390fe0459071b95
Roller-URL: https://ci.chromium.org/b/8827640557155883425
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827640557155883425
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I26970c01692cbd7fbe30fa3da7a35d5532118216
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/75340
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 b8f3ad2..390fe04 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b8f3ad2db9ad0f08970d62af3910f91ee5389e12
+Subproject commit 390fe0459071b952052a461ba758d7f880ecd273