[roll third_party/pigweed] pw_trace: timestamp_us should be a float

If the trace source has a nanosecond-resolution time source, the
timestamp_us needs to be a float.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126353

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 77adf069787e5e4..c7b11318ac76789
Roller-URL: https://ci.chromium.org/b/8792246450058616017
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1715b41f654ce1901f2375c867ad2b543ed39b4f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126412
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 77adf06..c7b1131 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 77adf069787e5e4da624350e7f8b0be2f69d413e
+Subproject commit c7b11318ac767898892dcca368cdcf447d639412