docs: Fix typo in configuring-zed.md (#42454)

Fix a minor typo in the setting key: `auto_install_extension` should be
`auto_install_extensions`.

Release Notes:

- N/A

docs/src/configuring-zed.md

@@ -213,7 +213,7 @@ Note: This setting has no effect in Vim mode, as rewrap is already allowed every
 ## Auto Install extensions
 
 - Description: Define extensions to be autoinstalled or never be installed.
-- Setting: `auto_install_extension`
+- Setting: `auto_install_extensions`
 - Default: `{ "html": true }`
 
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