tests: make goal-partkey-commands e2e-subs test serial

[algorandskiy]

Summary

goal-partkey-commands.sh fails time to time when checking one vs two node dirs for part keys. There is another test that creates/removed keys so parallel execution lead so flakiness as seen here. Fixed by moving goal-partkey-commands.sh into serial sub directory.

Test Plan

Existing tests should pass.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.26%. Comparing base (2a02530) to head (2c5c3b5).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6143      +/-   ##
==========================================
- Coverage   56.27%   56.26%   -0.01%     
==========================================
  Files         494      494              
  Lines       69943    69943              
==========================================
- Hits        39358    39353       -5     
- Misses      27910    27913       +3     
- Partials     2675     2677       +2     

Flag	Coverage Δ
	56.26% <ø> (?)

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[jannotti]

It would be nice to include the explanation for why this is under serial, but it doesn't matter too much, I suppose.