[Community]: Fix - Open AI Whisper client.audio.transcriptions returning Text Object which raises error (#25271)

- **Description:** The following
[line](fd546196ef/libs/community/langchain_community/document_loaders/parsers/audio.py (L117))
in `OpenAIWhisperParser` returns a text object for some odd reason
despite the official documentation saying it should return `Transcript`
Instance which should have the text attribute. But for the example given
in the issue and even when I tried running on my own, I was directly
getting the text. The small PR accounts for that.
 - **Issue:** : #25218
 

I was able to replicate the error even without the GenericLoader as
shown below and the issue was with `OpenAIWhisperParser`

```python
parser = OpenAIWhisperParser(api_key="sk-fxxxxxxxxx",
                                            response_format="srt",
                                            temperature=0)

list(parser.lazy_parse(Blob.from_path('path_to_file.m4a')))
```

libs/community/langchain_community/document_loaders/parsers/audio.py

@@ -129,7 +129,9 @@ class OpenAIWhisperParser(BaseBlobParser):
                 continue
 
             yield Document(
-                page_content=transcript.text,
+                page_content=transcript.text
+                if not isinstance(transcript, str)
+                else transcript,
                 metadata={"source": blob.source, "chunk": split_number},
             )