Prevent metadata duplication (#969)

When the term Identifier is part of the metadata and used as source_identifier,
it resulted in the value getting put into the metadata twice. Calling uniq!
on the array removes any duplicate metadata, as there should never be a reason
for the same metadata to be on a record twice.

app/models/concerns/bulkrax/has_matchers.rb

@@ -65,6 +65,7 @@ def set_parsed_data(name, value)
 
       parsed_metadata[name] ||= []
       parsed_metadata[name] += Array.wrap(value).flatten
+      parsed_metadata[name].uniq!
     end
 
     def set_parsed_object_data(object_multiple, object_name, name, index, value)