fix: output serialization for replacementEditTool (#587)

# Motivation

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# Content

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# Testing

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- [ ] I have added tests for my changes
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---------

Co-authored-by: rushilpatel0 <171610820+rushilpatel0@users.noreply.github.com>

Author: rushilpatel0

src/codegen/extensions/langchain/tools.py

@@ -1,6 +1,5 @@
 """Langchain tools for workspace operations."""
 
-import json
 from typing import Callable, ClassVar, Literal, Optional
 
 from langchain_core.tools.base import BaseTool
@@ -462,7 +461,6 @@ def __init__(self, codebase: Codebase) -> None:
     def _run(self, pr_id: int) -> str:
         result = view_pr(self.codebase, pr_id)
         return result.render()
-        return json.dumps(result, indent=2)
 
 
 class GithubCreatePRCommentInput(BaseModel):
@@ -791,4 +789,4 @@ def _run(
             end=end,
             count=count,
         )
-        return json.dumps(result, indent=2)
+        return result.render()