Fix old name of script context in docs

The docs contain an example how to limit the scripting contexts allowed,
but the example used an outdated name for the scoring context.

closes elastic#44232

Author: rjernst

docs/reference/scripting/security.asciidoc

@@ -101,7 +101,7 @@ to be `none`.
 
 [source,yaml]
 ----
-script.allowed_contexts: search, update <1>
+script.allowed_contexts: score, update <1>
 ----
-<1> This will allow only search and update scripts to be executed but not
+<1> This will allow only scoring and update scripts to be executed but not
 aggs or plugin scripts (or any other contexts).