Fasta test file containing seatoxin reference sequences incorrectly named

### Description of feature

The test file for seatoxin reference sequences has a typo and needs to be renamed from `setoxin-ref.fa` to `seatoxin-ref.fa` (file [here](https://github.com/nf-core/test-datasets/blob/multiplesequencealign/testdata/setoxin-ref.fa). All instances referencing this file should be updated (e.g. samplesheet)