style: fix doubled word in Lake/CLI/Serve docstring

This PR fixes "is not not" → "is not" in the setupFile docstring.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alok

src/lake/Lake/CLI/Serve.lean

@@ -32,7 +32,7 @@ public def invalidConfigEnvVar := "LAKE_INVALID_CONFIG"
 
 /--
 Build the dependencies of a Lean file and print the computed module's setup as JSON.
-If `header?` is not not `none`, it will be used to determine imports instead of the
+If `header?` is not `none`, it will be used to determine imports instead of the
 file's own header.
 
 Requires a configuration file to succeed. If no configuration file exists, it