[roll third_party/pigweed] pw_protobuf_compiler: Use Python group for proto alias

This allows referring to pw_proto_library Python packages by
abbreviated labels (e.g. //foo:foo.python as //foo:python).

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/40140

third_party/pigweed Rolled-Commits: b90d9b29d82eccf..2c6c0ba11589fed
Roller-URL: https://ci.chromium.org/b/8850580254702465584
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8850580254702465584
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I5db4122ac6070ddd0d49edf94e2328402dc8ee19
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/40160
Reviewed-by: 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 b90d9b2..2c6c0ba 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b90d9b29d82eccf5703f7f2119220eea3f0bf961
+Subproject commit 2c6c0ba11589feda9e0c1a6215d227e8177f3840