fix subworkflow template jinja variable for subworkflow name

[mirpedrol]

Close #2432

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #2435 (b156469) into dev (6b20a81) will increase coverage by 0.07%.
Report is 27 commits behind head on dev.
The diff coverage is 20.83%.

@@            Coverage Diff             @@
##              dev    #2435      +/-   ##
==========================================
+ Coverage   71.07%   71.14%   +0.07%     
==========================================
  Files          87       87              
  Lines        9431     9431              
==========================================
+ Hits         6703     6710       +7     
+ Misses       2728     2721       -7     

Files Changed	Coverage Δ
nf_core/download.py	59.35% <20.83%> (ø)

... and 1 file with indirect coverage changes