[ISSUE-566] Initial fix for aarch64 linux build to correct char type mismatch error

[snazzer]

This seems to fix the char type mismatch I reported in https://github.com/data61/anonlink/issues/566 - would love for someone to check and see if it addresses the issue correctly.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.28%. Comparing base (dc93947) to head (2489169).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #596   +/-   ##
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  Coverage   94.28%   94.28%           
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  Files          16       16           
  Lines         805      805           
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  Hits          759      759           
  Misses         46       46