Importing duplicate subject/transcription IDs doesn't error

[zwolf]

When a subject is reused in a different workflow, usually in the case of a test project, the import into Tove from Caesar should cause an ID conflict in the database that raises an exception here:

tove/app/services/caesar_importer.rb

Lines 17 to 20 in 33ea06b

	# If a transcription with this id already exists, an exception will be raised
	new_transcription = Transcription.new(transcription_create_attrs)
	new_transcription.workflow = workflow
	new_transcription.save!

But while this seems to be failing, an exception isn't being raised, at least not as far as Sentry. This should be looked into so we can ensure that no data is getting clobbered on import or anything like that.