[roll third_party/pigweed] pw_tokenizer: Fix decode string size type

Clang is unnecessarily strict with its narrowing rules, add a cast
to size_t to avoid using a '-Wno-c++11-narrowing', which could
potentially hide legitimate problems.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/98267

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 82e526ca40e899d..5c9007f0b81d761
Roller-URL: https://ci.chromium.org/b/8811167174964702145
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8811167174964702145
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I6a1248e3026efde02b9b150e6a35bb83b62390e9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/98491
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 82e526c..5c9007f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 82e526ca40e899d5ebeb9cd1028a618f75961ca9
+Subproject commit 5c9007f0b81d7612501423c7dcd6594af7312785