[roll third_party/pigweed] pw_presubmit: Skip submodules in copyright check

This affected a downstream project that has not yet set up excludes. The
downstream project still needs to fix that, but this was an error
anyway.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/51420

third_party/pigweed Rolled-Commits: e1a9f4d64ff2b6a..7e4cf8047992d46
Roller-URL: https://ci.chromium.org/b/8843138134485768016
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8843138134485768016
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I38172e99d039cd16beb4b6013245ac1d90aad323
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/51461
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 e1a9f4d..7e4cf80 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e1a9f4d64ff2b6ac27b2f8f4ed9a84a9897224d4
+Subproject commit 7e4cf8047992d4665a78336591ff133779874b1f