iteritems deprecation warning on merge_seqs

[lxsteiner]

Related to #290
In qiime2-amplicon-2024.2 I get a similar warning with merge_seqs:

>>> silva_extended_seqs, = merge_seqs([v34_organelle_seqs, v34_silva_seqs])
/.../.conda/envs/qiime2-juypterlab_env/lib/python3.8/site-packages/q2_types/feature_data/_transformer.py:258: FutureWarning: iteritems is deprecated and will be removed in a future version. Use .items instead.
  for id_, seq in data.iteritems():

Cheers

[colinvwood]

looks like this was fixed in #323