Fix syntax error in shield stack

[Zharktas]

for .. in for lists produces indexes, for .. of produces actual elements.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 23.27%. Comparing base (f11c702) to head (7121c91).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2185   +/-   ##
=======================================
  Coverage   23.27%   23.27%           
=======================================
  Files          42       42           
  Lines        6054     6054           
  Branches       35       35           
=======================================
  Hits         1409     1409           
  Misses       4645     4645           

Flag	Coverage Δ
cdk	91.89% <ø> (ø)

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