Add a version of the payload for CodeContext

Add the payload "42*42" to the fuzzing list in order to cover the "Code context" detection point mentioned in the https://portswigger.net/web-security/server-side-template-injection training

Fuzzing/template-engines-expression.txt

@@ -1,3 +1,4 @@
+42*42
 {42*42}
 {{42*42}}
 {{{42*42}}}