[roll third_party/pigweed] pw_transfer: Use project-absolute imports for test fixture

Importing test_fixture.py as a relative import doesn't work in the 7.0.0
release candidate of Bazel. This changes the paths to be
project-absolute to unblock updating Bazel.

Original-Bug: b/310038737
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/180390

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 563393f56a8c41b..8b0de7e74e763ba
Roller-URL: https://ci.chromium.org/b/8764794047966576449
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I5714747bfcdfb033d568c98fb9f252feefb8b049
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/180470
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 563393f..8b0de7e 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 563393f56a8c41b03aed3e99e37993fb1c5c0dc8
+Subproject commit 8b0de7e74e763ba9a8303186383ee8866a677000