"SaveAudioMP3" node DOES NOT adhere to Save File Formatting rules in its filename_prefix widget

### Custom Node Testing

- [ ] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

1. You put this text into the `filename_prefix` widget of **Save Audio (MP3)** node: _"audio/ACE-S_Audio-%KSampler.sampler_name%-"_ expecting the node to adhere to **[Save File Formatting](https://blenderneko.github.io/ComfyUI-docs/Interface/SaveFileFormatting/)** documentation.

2. The generated audio file should be saved in a folder called "audio" with a name looking like this: _"ACE-S_Audio-euler_ancestral-0001.mp3"_

### Actual Behavior

1. You put this text into the `filename_prefix` widget of **Save Audio (MP3)** node: _"audio/ACE-S_Audio-%KSampler.sampler_name%-"_ expecting the node to adhere to **[Save File Formatting](https://blenderneko.github.io/ComfyUI-docs/Interface/SaveFileFormatting/)** documentation.

2. The generated audio file is saved in a folder called "audio" with an a name like this: _"ACE-S_Audio-%KSampler.sampler_name%-0001.mp3"_

### Steps to Reproduce

1. You put this text into the `filename_prefix` widget of **Save Audio (MP3)** node: _"audio/ACE-S_Audio-%KSampler.sampler_name%-"_.

2. The generated audio file should be saved in a folder called "audio".

### Debug Logs

```powershell
[INFO] got prompt
[INFO] Requested to load ACE15TEModel_
[INFO] Model ACE15TEModel_ prepared for dynamic VRAM loading. 9126MB Staged. 0 patches attached. Force pre-loaded 258 weights: 511 KB.

LM sampling: 0%| | 0/300 [00:00