Add Lithuanian and Marathi to TextToSpeechLanguage

[owen-airbnb]

Lithuanian and Marathi are supported per https://developer.vonage.com/en/voice/voice-api/concepts/text-to-speech#voice-names but are not present in the TextToSpeechLanguage enum. Add them.

Contribution Checklist

• Unit tests!
• Updated CHANGELOG.md

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.87%. Comparing base (ff6decc) to head (699b4d7).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #603   +/-   ##
=========================================
  Coverage     99.87%   99.87%           
  Complexity     3421     3421           
=========================================
  Files           516      516           
  Lines          7374     7376    +2     
  Branches        411      411           
=========================================
+ Hits           7365     7367    +2     
  Misses            3        3           
  Partials          6        6           

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