doc: fix heading level in errors.md

PR-URL: #21618
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>

Author: vsemozhetbyt

doc/api/errors.md

@@ -457,7 +457,7 @@ added properties.
 
 ### Class: SystemError
 
-### error.info
+#### error.info
 
 `SystemError` instances may have an additional `info` property whose
 value is an object with additional details about the error conditions.