teeny gramatical error in docs (#12908)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Incorrect use of the indefinite article- 'an project' instead of 'a
project'

## Test Plan

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Was not tested due to it being a small change to docs wording without
change in formatting.

Author: dasAtRagedy

docs/guides/integration/fastapi.md

@@ -42,7 +42,7 @@ To use uv with this application, inside the `project` directory run:
 $ uv init --app
 ```
 
-This creates an [project with an application layout](../../concepts/projects/init.md#applications)
+This creates a [project with an application layout](../../concepts/projects/init.md#applications)
 and a `pyproject.toml` file.
 
 Then, add a dependency on FastAPI: