FastQC: Avoid NXF langserver warning (#7069)

New Nextflow language server throws a warning about this variable as it's unused. Prefixing with an underscore resolves this.

modules/nf-core/fastqc/main.nf

@@ -24,7 +24,7 @@ process FASTQC {
     // Make list of old name and new name pairs to use for renaming in the bash while loop
     def old_new_pairs = reads instanceof Path || reads.size() == 1 ? [[ reads, "${prefix}.${reads.extension}" ]] : reads.withIndex().collect { entry, index -> [ entry, "${prefix}_${index + 1}.${entry.extension}" ] }
     def rename_to = old_new_pairs*.join(' ').join(' ')
-    def renamed_files = old_new_pairs.collect{ old_name, new_name -> new_name }.join(' ')
+    def renamed_files = old_new_pairs.collect{ _old_name, new_name -> new_name }.join(' ')
 
     // The total amount of allocated RAM by FastQC is equal to the number of threads defined (--threads) time the amount of RAM defined (--memory)
     // https://github.com/s-andrews/FastQC/blob/1faeea0412093224d7f6a07f777fad60a5650795/fastqc#L211-L222