[roll third_party/pigweed] docs: Updated darkmode colors for pigweed.dev

These color changes lower the contrast slightly for pigweed.dev
darkmode.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/149614

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: d8a333554ce7b4b..afb69025189a257
Roller-URL: https://ci.chromium.org/b/8779468326046119553
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ic04567d65c6896f23b01ed2df674705e357b1620
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/149933
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 d8a3335..afb6902 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d8a333554ce7b4b646e4c2420014e787152d90cf
+Subproject commit afb69025189a257b9cfd6cafb5747ee05183b104