Ignore missing docker client in Docker system check

Codecov Report

Merging #245 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #245      +/-   ##
==========================================
+ Coverage   78.63%   78.65%   +0.02%     
==========================================
  Files         151      151              
  Lines        8920     8929       +9     
==========================================
+ Hits         7014     7023       +9     
  Misses       1906     1906

Impacted Files	Coverage Δ
arkindex/project/tests/test_checks.py	100% <100%> (ø)
arkindex/project/checks.py	76% <100%> (+0.39%)

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merged

mentioned in commit 34361e8c