[roll third_party/pigweed] pw_rpc: Fix __repr__ for UnaryResponse in Python client

UnaryResponse.__repr__ should only call proto_repr when it has a
response.

Original-Fixes: b/247127597
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/110970

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: bcd53dbe356f9b8..55f7eca400f7cdb
Roller-URL: https://ci.chromium.org/b/8802567455843370449
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I961f34530759a63b3c1b3a2a2276dfb6cc657339
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/110959
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 bcd53db..55f7eca 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit bcd53dbe356f9b85e05a753d37f5bafc44fdff3a
+Subproject commit 55f7eca400f7cdb82e1f2327096f7c3c48365788