Don't exit modules install when no commit hash is found

[KevinMenden]

Issue a warning when we can't get the git_sha for a module instead of raising a warning and exiting.
This way the modules.json get's created and we can continue installing modules.
The linting still warns about missing entires in the modules.json.

[codecov]

Codecov Report

Merging #1174 (f6cb3ed) into dev (1408310) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##              dev    #1174      +/-   ##
==========================================
+ Coverage   70.56%   70.58%   +0.01%     
==========================================
  Files          48       48              
  Lines        5117     5116       -1     
==========================================
  Hits         3611     3611              
+ Misses       1506     1505       -1     

Impacted Files	Coverage Δ
nf_core/modules/module_utils.py	45.18% <0.00%> (+0.33%)	⬆️

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[ErikDanielsson]

Nice! Seems to work for me also! 👍