Add unicode generation to IWSLT tests (followup to #1608)

[Nayef211]

• Followup to [WIP] add unicode generation to IWSLT tests  #1608
• Addresses [META] Add missing unicode generation for IWSLTs #1607

Testing

• pytest test_iwslt2016.py
• pytest test_iwslt2017.py

[codecov]

Codecov Report

Merging #1642 (ab553b7) into main (7209421) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1642   +/-   ##
=======================================
  Coverage   85.58%   85.58%           
=======================================
  Files          58       58           
  Lines        2497     2497           
=======================================
  Hits         2137     2137           
  Misses        360      360           

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[parmeet]

LGTM! Thanks for fixing this. I think this is the reason for random test failure.