chore: Install git-annex from PyPI

[effigies]

Conda ran into problem a bit ago, and we don't need it here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.74%. Comparing base (26771dd) to head (cc7a4ed).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #291      +/-   ##
==========================================
+ Coverage   96.72%   96.74%   +0.01%     
==========================================
  Files          16       16              
  Lines        1984     1994      +10     
  Branches      223      267      +44     
==========================================
+ Hits         1919     1929      +10     
  Misses         41       41              
  Partials       24       24              

Flag	Coverage Δ
unittests	96.72% <ø> (ø)

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