[roll third_party/pigweed] pw_rpc: Temporarily provide default abandon() implementation

The default implementation of abandon() allows users to update in a
non-breaking way. The default implementation will be removed once the
migration is complete.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/97682

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 8d399a854276d2b..c294be0b0ac9f3d
Roller-URL: https://ci.chromium.org/b/8811790414774057121
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811790414774057121
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I9fdb3241113acd7274df1aab3d1eeb050ae4f627
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/97674
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 8d399a8..c294be0 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 8d399a854276d2ba344f0827a7a7b95a979c1a7a
+Subproject commit c294be0b0ac9f3dde0aaeec38436acead10d4f52