[Doc]Update Qwen3-Omni-30B-A3B-Thinking.md (#8669)

### What this PR does / why we need it?
apt-get install ffmpeg -y -> apt-get install -y ffmpeg

Signed-off-by: tanhaoan333 <tanhaoan@huawei.com>

docs/source/tutorials/models/Qwen3-Omni-30B-A3B-Thinking.md

@@ -73,7 +73,7 @@ Please install system dependencies
 ```bash
 pip install qwen_omni_utils modelscope
 # Used for audio processing.
-apt-get update && apt-get install ffmpeg -y
+apt-get update && apt-get install -y ffmpeg
 # Check the installation.
 ffmpeg -version
 ```