Swift: Fix codegen error

Author: jketema

swift/ql/.generated.list

@@ -5,6 +5,7 @@ private import codeql.swift.generated.AvailabilitySpec
  * be referenced directly.
  */
 module Impl {
+  // the following QLdoc is generated: if you need to edit it, do it in the schema file
   /**
    * An availability spec, that is, part of an `AvailabilityInfo` condition. For example `iOS 12` and `*` in:
    * ```