Announce test_clone_datasets_root xfail on github osx

[yarikoptic]

To make daily runs clearer to not mask some real issue.

ref:

• test_clone_datasets_root: fails some times on OSX #7485

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (9942bf4) 91.52% compared to head (178a233) 91.52%.

Additional details and impacted files

@@           Coverage Diff           @@
##            maint    #7489   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files         325      325           
  Lines       43441    43443    +2     
  Branches     5827     5827           
=======================================
+ Hits        39761    39763    +2     
  Misses       3665     3665           
  Partials       15       15           

Files Changed	Coverage Δ
datalad/core/distributed/tests/test_clone.py	98.43% <100.00%> (+<0.01%)	⬆️
datalad/tests/utils_pytest.py	89.28% <100.00%> (+0.01%)	⬆️

... and 1 file with indirect coverage changes

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[yarikoptic]

OSX fail is unrelated actually:

FAILED ../local/tests/test_diff.py::test_path_diff - datalad.runner.exception.CommandError: CommandError: 'git -c diff.ignoreSubmodules=none -c core.quotepath=false annex find --anything --include '*' --json --json-error-messages -c annex.dotfiles=true' failed with exitcode 139 under /private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/datalad_temp_test_path_difffyi0kc7_/subds_modified [info keys: stdout_json] [err: 'error: git-annex died of signal 11']

filed #7490 .

benchmarks unrelated

[yarikoptic-gitmate]

PR released in 0.19.4