[audio] make some tests deterministic to avoid flakiness

[racoiaws]

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What does this PR do ?

Some tests failed randomly, so I'm adding a local rng to torch.randn calls to avoid that

Collection: [Audio]

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Additional Information

• Related to
  • [audio] Adding tests for predictive models #12823
  • [audio] Tests for mask models #12913
  • testss: Disable flaky test #13083

[chtruong814]

Merging this now to resolve some current issues