doc: close tag in n-api.md

PR-URL: nodejs#42751
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>

doc/api/n-api.md

@@ -1191,6 +1191,7 @@ added:
 NAPI_EXTERN napi_status node_api_throw_syntax_error(napi_env env,
                                                     const char* code,
                                                     const char* msg);
+```
 
 * `[in] env`: The environment that the API is invoked under.
 * `[in] code`: Optional error code to be set on the error.