api: binhost: use throw away bucket for tests

This code doesn't actually access the bucket, but since it's not a
real one even though it looks like it might/could be, switch to the
trash bucket to avoid confusion.

BUG=chromium:1481176
TEST=CQ passes

Change-Id: I4f7e6a96f2b6849849c675d93709f6b864093a24
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4856684
Commit-Queue: Alex Klein <saklein@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/api/controller/binhost.py b/api/controller/binhost.py
index 8d9f533..44554bf 100644
--- a/api/controller/binhost.py
+++ b/api/controller/binhost.py
@@ -41,7 +41,7 @@
     """Add fake binhosts to a successful response."""
     new_binhost = output_proto.binhosts.add()
     new_binhost.uri = (
-        "gs://cr-prebuilt/board/amd64-generic/"
+        f"{constants.TRASH_BUCKET}/board/amd64-generic/"
         "paladin-R66-17.0.0-rc2/packages/"
     )
     new_binhost.package_index = "Packages"