[roll third_party/pigweed] pw_watch: Close with terminate() instead of kill()

Closing with SIGTERM allows the subprocess to clean up. In this past,
SIGKILL was used because the Ninja build files are sometimes removed if
the build is interrupted. pw watch automatically re-runs gn gen when
necessary, so the Ninja build files will be regenerated as needed.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/68740

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 9a5210dc2b50081..3be4c9e5fd97733
Roller-URL: https://ci.chromium.org/b/8830472591263924145
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8830472591263924145
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I044110b0d0585728956b6acfe94746066e0f1c08
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/68904
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 9a5210d..3be4c9e 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 9a5210dc2b5008149e774fb1dd756d78e2630319
+Subproject commit 3be4c9e5fd97733244495c9d04f33aafa46fe0c5