Add const_finder.dart.snapshot to the artifacts to be copied over.

Flutter has added a new utility called const finder which requires a
snapshot that matches the engine version. This is uploaded by the
engine as an artificat and we need to do the same in the HHH bot to
ensure the correct version of the snapshot is avaialable.

Change-Id: Ic5dacfc6f51a4ca7776ce5e308f92e67e6a2214b
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/147684
Reviewed-by: Alexander Aprelev <aam@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
3 files changed