Fix depset/list confusion in #7458.
Fix depset/list confusion in #7458.

See
https://github.com/protocolbuffers/protobuf/pull/7458#issuecomment-633147682.

release notes: no

Signed-off-by: Harvey Tuch <c185081708e02336640916420d0c772668570de5@google.com>

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf