roll: third_party/pigweed pw_unit_test: Fix failing test with latest GN

With the latest version of GN, the test_group_metadata_test was
failing to resolve the TARGET_FILE due to no output files.

Clean this up by using the target_out_dir directly instead of the
indirect TARGET_FILE method.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/236439
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: b1facaf899336bcf653e3113ef7cee188e77e0f0

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: d5fcc90b39ee75..b1facaf899336b
Roller-URL: https://ci.chromium.org/b/8736447310557041121
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I0147f13e4ff64ab9b7f85f9fdfc8b38caf0c760e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/236752
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.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 d5fcc90..b1facaf 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d5fcc90b39ee7568855390535fa854cea8f33c95
+Subproject commit b1facaf899336bcf653e3113ef7cee188e77e0f0