[roll pigweed] pw_tokenizer: Limit files being parsed to CSVs

- Create a check to only parse CSVs in the directory

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/107645

https://pigweed.googlesource.com/pigweed/pigweed
pigweed Rolled-Commits: 4c01e58701501bc..fe1681d9ab676ec
Roller-URL: https://ci.chromium.org/b/8805354714191236993
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I873b0f9cb1eef06708235162db6906613a28067a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/zephyr-integration/+/107677
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/pigweed b/pigweed
index 4c01e58..fe1681d 160000
--- a/pigweed
+++ b/pigweed
@@ -1 +1 @@
-Subproject commit 4c01e58701501bc84bd7b4b7c4cfdb43c1b37636
+Subproject commit fe1681d9ab676ec2b1ada6404030c9d7fa100185