Skip tests when ran as root

[adswa]

There were a handful of tests reported in #525 that failed when ran as root. This PR implements the proposed solution to skip these tests when ran as root, using a preexisting pytest util from datalad-core.

fixes #525

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (97b373c) 92.44% compared to head (98ac8a8) 92.59%.
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #593      +/-   ##
==========================================
+ Coverage   92.44%   92.59%   +0.15%     
==========================================
  Files         149      151       +2     
  Lines       10783    11119     +336     
  Branches     1617     1653      +36     
==========================================
+ Hits         9968    10296     +328     
- Misses        638      642       +4     
- Partials      177      181       +4     

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[mih]

Thanks for taking care of this issue! The approach makes sense.