Make empty gzipped fastq file for subsample stub

Work around for nf-test bug with .fastq.gz files that aren't gzipped

Co-authored-by: Simon Pearce <[email protected]>

Author: dwells-eit

modules/nf-core/autocycler/subsample/main.nf

@@ -43,7 +43,7 @@ process AUTOCYCLER_SUBSAMPLE {
     """
 
     mkdir $prefix
-    touch ${prefix}/sample_00.fastq.gz
+    echo | gzip > ${prefix}/sample_00.fastq.gz
 
     cat <<-END_VERSIONS > versions.yml
     "${task.process}":