perf(stt-whisper): close the audio file handle after calling the OpenAI transcription API (#8528)

* 在调用 OpenAI API 后关闭文件句柄再删除临时文件。

核心问题：whisper_api_source.py 第 121 行用 open(audio_url, "rb") 打开文件后，文件句柄没有被关闭，导致 Windows 上报 "另一个程序正在使用此文件" 的错误，temp wav 文件无法删除。
修复方案：在调用 OpenAI API 后关闭文件句柄再删除临时文件。

* fix(whisper_api): use context manager for audio file handling to ensure proper closure

---------

Co-authored-by: Soulter <905617992@qq.com>

Author: tjc6666666666666

astrbot/core/provider/sources/whisper_api_source.py

@@ -116,10 +116,11 @@ async def get_text(self, audio_url: str) -> str:
 
                 audio_url = output_path
 
-        result = await self.client.audio.transcriptions.create(
-            model=self.model_name,
-            file=("audio.wav", open(audio_url, "rb")),
-        )
+        with open(audio_url, "rb") as audio_file:
+            result = await self.client.audio.transcriptions.create(
+                model=self.model_name,
+                file=("audio.wav", audio_file),
+            )
 
         # remove temp file
         if output_path and os.path.exists(output_path):