[roll third_party/pigweed] pw_protobuf: Don't encode fields with default (zero) values

For better compatibility with other encoders, do not encode zero values
of fixed and varint fields.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/91661

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ee7729707ce0551..fd7c677ca6e4d8c
Roller-URL: https://ci.chromium.org/b/8811710434878013489
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811710434878013489
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I53952f97c3bc0ab273c2df12d9363e3f1b616045
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/97789
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 ee77297..fd7c677 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ee7729707ce0551541a9e1f6152aa8fd246f956e
+Subproject commit fd7c677ca6e4d8cab04bdc12028e6fd36632e131