clean up more dict iter warnings

Newer pylint catches more cases where we use dicts fields but outside
of an obvious iteration.  Force them through list() as makes sense.

BUG=chromium:1015273
TEST=`cros lint` is clean

Change-Id: I28207a7b5c1400b70094c67ba138be8d7b07a771
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1870893
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Michael Mortensen <mmortensen@google.com>
diff --git a/api/controller/toolchain.py b/api/controller/toolchain.py
index e673b51..faf3646 100644
--- a/api/controller/toolchain.py
+++ b/api/controller/toolchain.py
@@ -30,7 +30,7 @@
 
 @faux.all_empty
 @validate.require('build_target.name')
-@validate.is_in('artifact_type', _NAMES_FOR_ARTIFACTS.keys())
+@validate.is_in('artifact_type', _NAMES_FOR_ARTIFACTS)
 @validate.validation_complete
 def UpdateEbuildWithAFDOArtifacts(input_proto, output_proto, _config):
   """Update Chrome or kernel ebuild with most recent unvetted artifacts.
@@ -48,7 +48,7 @@
 
 @faux.all_empty
 @validate.require('build_target.name')
-@validate.is_in('artifact_type', _NAMES_FOR_ARTIFACTS.keys())
+@validate.is_in('artifact_type', _NAMES_FOR_ARTIFACTS)
 @validate.validation_complete
 def UploadVettedAFDOArtifacts(input_proto, output_proto, _config):
   """Upload a vetted orderfile to GS bucket.