sourmash sig extract doesn't respect - for stdin?

[ctb]

Per @luizirber,

a bit disappointed I had to use /dev/stdin instead of - in sourmash sig extract

for sig in GCF_000006945.2 GCF_000012345.1 GCF_000015665.1 GCF_000182965.3      
GCF_001890705.1 GCF_002251655.1 GCF_021117135.1                                 
do                                                                              
curl -L https://wort.sourmash.bio/v1/view/genomes/${sig} | \                    
pixi exec -s sourmash-minimal sourmash sig extract -k 21 /dev/stdin -o          
${sig}.sig                                                                      
done