fix openai image schema bug

[usamimeri]

User description

I try to run android assistant with gpt-4-turbo, but there was an error indicating the messages schema was incorrect:
"Invalid type for 'messages[1].content[1].image_url': expected an object, but got a string instead
by checking the openai-sdk doc https://platform.openai.com/docs/guides/vision and https://platform.openai.com/docs/api-reference/chat/create
"I found that the format {"type":"image_url","image_url":YOUR_IMAGE_URL} can be used on gpt-4-vision-preview, but not on gpt-4-turbo, whereas the format {"type":"image_url","image_url":{"url":YOUR_IMAGE_URL}} can be used on both."

Consequently, I update the schema for more compability.

[qodo-merge-pro]

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PR Description updated to latest commit (82b4be5)

• Copy walkthrough table to "Files Changed" Tab

[qodo-merge-pro]

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PR Review 🔍

⏱️ Estimated effort to review [1-5]	2, because the PR involves a simple and straightforward change in the data structure of an image URL within a single method. The change is localized and does not appear to affect other parts of the codebase.
🧪 Relevant tests	No
⚡ Possible issues	Data Type Consistency: Ensure that all calling functions or methods that use _user_msg_with_imgs are updated to handle the new object structure for image_url instead of a string. If not, this could lead to runtime errors.
🔒 Security concerns	No

[qodo-merge-pro]

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PR Code Suggestions ✨

Category	Suggestion	Score
Possible bug	Correct the structure of the dictionary to properly format the image URL The dictionary key for "image_url" is incorrectly nested within another dictionary. This might lead to unexpected behavior when accessing the "url". The "image_url" key should directly contain the "url" value. metagpt/provider/base_llm.py [68] -content.append({"type": "image_url", "image_url": {"url": url}}) +content.append({"type": "image_url", "image_url": url}) Suggestion importance[1-10]: 10 Why: The suggestion correctly identifies a critical issue where the dictionary structure for "image_url" was changed in a way that could break functionality. The suggested fix restores the correct dictionary structure, ensuring the code functions as intended.	10

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 70.20%. Comparing base (f201b2f) to head (82b4be5).

Files	Patch %	Lines
metagpt/provider/base_llm.py	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1268      +/-   ##
==========================================
- Coverage   70.22%   70.20%   -0.03%     
==========================================
  Files         316      316              
  Lines       18860    18860              
==========================================
- Hits        13245    13240       -5     
- Misses       5615     5620       +5     

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[better629]

lgtm