chore(docs): Update v0.16.0 release date in changelog

[tgasser-nv]

Description

Related Issue(s)

Checklist

• I've read the CONTRIBUTING guidelines.
• I've updated the documentation if applicable.
• I've added tests if applicable.
• @mentions of the person or team responsible for reviewing proposed changes.

[github-actions]

Documentation preview

https://nvidia.github.io/NeMo-Guardrails/review/pr-1377

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.62%. Comparing base (957a5de) to head (2f82d20).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1377   +/-   ##
========================================
  Coverage    71.62%   71.62%           
========================================
  Files          171      171           
  Lines        17021    17021           
========================================
  Hits         12192    12192           
  Misses        4829     4829           

Flag	Coverage Δ
python	71.62% <ø> (ø)

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