[roll third_party/pigweed] pw_rpc: Support listening to responses in Python client

Add an open() call to the Python RPC client alongside invoke(). Open
ignores errors when sending the initial RPC request. This can be used to
listen for responses from an RPC that was not explicitly requested. This
is helpful when an RPC server cannot be immediately reached (e.g. the
device isn't plugged in yet).

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/59640

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 478d3f2aa08f6d4..6d7317260b3bc08
Roller-URL: https://ci.chromium.org/b/8836598739793076945
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8836598739793076945
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I6af4372ebe28a77c31eb05819d0ef4c267fbcacb
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/60322
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 478d3f2..6d73172 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 478d3f2aa08f6d4c1b7167d1e949c58b64317166
+Subproject commit 6d7317260b3bc088860290d5611558d1e74d7af6