Fix typo in backends.mdx documentation (#1213)

## Overview
Changed Aautomatic to Automatic and matched the sentences context

## Type of change

**Type:** Fix typo

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## Checklist
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- [x] I have read the [contributing guidelines](README.md)
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## Additional notes
Its my first PR for langchain, I love the framework and wanted to give
back in any way possible!

Author: dhruv1710

src/oss/deepagents/backends.mdx

@@ -43,7 +43,7 @@ agent = create_deep_agent(
 
 **Best for:**
 - A scratch pad for the agent to write intermediate results.
-- Aautomatic eviction of large tool outputs which the agent can then read back in piece by piece.
+- Automatic eviction of large tool outputs which the agent can then read back in piece by piece.
 
 ### FilesystemBackend (local disk)