BUG: improve error message formatting in `feature-table tabulate-seqs`

[lizgehret]

Bug Description When running feature-table tabulate-seqs, it's possible to generate the following error using the PD Mice data when using the default merge method of strict:

The error message is correct, but the formatting looks clunky due to an unnecessary newline.

Steps to reproduce the behavior

1. Download the following artifacts from the PD Mice tutorial:

   • dada2_rep_set.qza
   • taxonomy.qza
   • bespoke_taxonomy.qza

2. Keeping all of the above artifacts in the same working directory, put the two taxonomy artifacts into a sub directory of your choice (e.g. multi-taxonomy/ or something like that)

3. Run the following command (using a QIIME 2 Amplicon 2023.9 environment):

   qiime feature-table tabulate-seqs \
   --i-data dada2_rep_set.qza \
   --i-taxonomy multi-taxonomy/ \
   --o-visualization dada2_multi_taxonomy.qzv \
   --verbose

   The error in the above screenshot will be displayed (since the --p-merge-method has a default of strict).

Expected behavior This isn't strictly a bug, but the formatting of the error message looks a bit weird, and can be fixed with an updated multi-line string.

I'll leave the rest to you to figure out @hagenjp 😉