[DOCS] Fixes 6.4 breaking change page

Author: lcawl

docs/reference/migration/migrate_6_4.asciidoc

@@ -28,9 +28,10 @@ to follow up the operation with a request to adjust to the desired settings on
 the target index, or send the desired value of these settings with the resize
 operation.
 
+[[breaking_64_scripting_changes]]
 === Scripting
 
-===== Legacy stored script formats have been deprecated
+==== Legacy stored script formats have been deprecated
 
 Stored script formats that don't use top level `script` object have been deprecated and
 support for these formats will be removed in the next major release.