parakeet : update parakeet test models generation

This commit updates the parakeet test models to ensure that the random
values generated for mel filters are not negative. This will otherwise
cause a debug assertion and fail the parakeet-test.

Refs: https://github.com/ggml-org/whisper.cpp/actions/runs/30547589734/job/90887624319?pr=3962

models/generate-parakeet-test-model.py

@@ -86,7 +86,8 @@ def generate(output_path, n_fft_override=None):
 
         fout.write(struct.pack("i", n_mels))
         fout.write(struct.pack("i", n_freqs))
-        f32(n_mels, n_freqs).tofile(fout)
+        # Mel filter must be non-negative.
+        np.abs(f32(n_mels, n_freqs)).tofile(fout)
 
         fout.write(struct.pack("i", n_fft))
         f32(n_fft).tofile(fout)