roll: third_party/pigweed: pw_rpc: Expand comment for internal::ClientServerTestComment

Direct readers to the public version of the class.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/220574
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 40ced78e4ae4490..3178503b13226d7
Roller-URL: https://ci.chromium.org/b/8742948280656637905
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ic3c4ef2cf0795d7ebe1289457608db3c6b393c5f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/220653
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 40ced78..3178503 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 40ced78e4ae4490c6c429257717f08da30700a25
+Subproject commit 3178503b13226d74c74c3902ea68e5df2147c825