BF(TST): Skip testing for having PID listed if no psutil

[yarikoptic]

Closes #5918

An alternative (or complimentary) would be to move psutil from
devel extra depends to some component of default install_requires dependencies, WDYT?

Meanwhile, addressing on datalad/git-annex by installing it: datalad/git-annex#75

[codecov]

Codecov Report

Merging #5920 (df8fa8b) into maint (d1a19e2) will decrease coverage by 5.43%.
The diff coverage is 33.33%.

❗ Current head df8fa8b differs from pull request most recent head 5a463dd. Consider uploading reports for the commit 5a463dd to get more accurate results

@@            Coverage Diff             @@
##            maint    #5920      +/-   ##
==========================================
- Coverage   90.26%   84.82%   -5.44%     
==========================================
  Files         300      297       -3     
  Lines       42513    42498      -15     
==========================================
- Hits        38373    36048    -2325     
- Misses       4140     6450    +2310     

Impacted Files	Coverage Δ
datalad/support/tests/test_locking.py	91.75% <33.33%> (-1.87%)	⬇️
datalad/support/tests/utils.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/metadata/extractors/tests/test_audio.py	19.35% <0.00%> (-80.65%)	⬇️
datalad/metadata/extractors/xmp.py	12.96% <0.00%> (-79.63%)	⬇️
datalad/metadata/extractors/exif.py	18.75% <0.00%> (-78.13%)	⬇️
datalad/metadata/extractors/image.py	19.35% <0.00%> (-77.42%)	⬇️
datalad/metadata/extractors/audio.py	20.00% <0.00%> (-77.15%)	⬇️
datalad/metadata/extractors/tests/test_exif.py	24.00% <0.00%> (-76.00%)	⬇️
datalad/metadata/extractors/tests/test_xmp.py	26.92% <0.00%> (-73.08%)	⬇️
datalad/metadata/extractors/tests/test_image.py	26.92% <0.00%> (-73.08%)	⬇️
... and 94 more

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[yarikoptic]

IMHO trivial, let's proceed.