squeeze out None licenses

[ocefpaf]

Grayskull crashes when one of the licenses is None in the all_license_name list. This is probably not the best solution but I thought I should try a PR instead of just opening issues ;-p

[marcelotrevisani]

Cool! Thanks for that! :)

[codecov-commenter]

Codecov Report

Merging #392 (30a4b58) into main (9c3242e) will increase coverage by 0.70%.
The diff coverage is 92.82%.

@@            Coverage Diff             @@
##             main     #392      +/-   ##
==========================================
+ Coverage   91.30%   92.01%   +0.70%     
==========================================
  Files          17       16       -1     
  Lines        1576     1703     +127     
==========================================
+ Hits         1439     1567     +128     
+ Misses        137      136       -1     

Flag	Coverage Δ
unittests	92.01% <92.82%> (+0.70%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
grayskull/base/github.py	72.83% <72.83%> (ø)
grayskull/license/discovery.py	94.87% <78.12%> (-2.28%)	⬇️
grayskull/strategy/abstract_strategy.py	83.33% <83.33%> (ø)
grayskull/__main__.py	95.60% <93.18%> (-2.55%)	⬇️
grayskull/base/factory.py	91.17% <93.33%> (+1.17%)	⬆️
grayskull/strategy/py_base.py	95.00% <95.00%> (ø)
grayskull/config.py	96.96% <96.96%> (ø)
grayskull/utils.py	98.12% <97.58%> (-1.88%)	⬇️
grayskull/strategy/pypi.py	97.68% <97.68%> (ø)
... and 7 more

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