Bug: 'str' object has no attribute 'pop'

### Browser Use Version

0.12.0

### Bug Description, Steps to Reproduce, Screenshots

When using the latest version of browser use (0.12.0), running the example script yields an error
Usage model: Gemini
error screenshot：
<img width="982" height="143" alt="Image" src="https://github.com/user-attachments/assets/fd59d1fc-009c-4cbd-8d12-ddb900e58ebb" />
Additional note: Currently, I have been downgraded to 0.11.13 and am using it normally

### Failing Python Code

```python
from browser_use import Agent, ChatGoogle
from dotenv import load_dotenv
import asyncio

load_dotenv()

async def main():
    llm = ChatGoogle(model="gemini-flash-latest")
    task = "Find the number 1 post on Show HN"
    agent = Agent(task=task, llm=llm)
    await agent.run()

if __name__ == "__main__":
    asyncio.run(main())
```

### LLM Model

Most Gemini

### Operating System & Browser Versions

window10

### Full DEBUG Log Output

```shell
ERROR    [5-flash] 💥 API call failed after 0.09s: AttributeError: 'str' object has no attribute 'pop'
WARNING  [Agent] ⚠️ LLM error (ModelProviderError: 'str' object has no attribute 'pop') but no fallback_llm co
nfigured
WARNING  [Agent] ❌ Result failed 1/6 times: 'str' object has no attribute 'pop'
```

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