chore(tests): stabilize tts test

[mudler]

Description

This PR tries to stabilize tests that currently are failing on master:

 API test Model gallery [It] installs and is capable to run tts [tts]
/home/runner/work/LocalAI/LocalAI/core/http/app_test.go:681

  [FAILED] Expected
      <string>: audio/vnd.wave
  to equal
      <string>: audio/x-wav
  In [It] at: /home/runner/work/LocalAI/LocalAI/core/http/app_test.go:707 @ 12/16/24 15:19:51.986

Notes for Reviewers

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