Use self.poutput() instead of print() in arg_print.py example

[tleonhardt]

Minor tweak to the arg_print.py example to make it use poutput() instead of print().

[codecov]

Codecov Report

Merging #298 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #298   +/-   ##
=======================================
  Coverage   89.89%   89.89%           
=======================================
  Files           1        1           
  Lines        1514     1514           
=======================================
  Hits         1361     1361           
  Misses        153      153

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