fix(learn): Convert response testcase regex handles any variable name (#40568)

* Update convert response to JSON testcase

Testcase previously required that variable be named exactly "response". Changes will allow variable of any name to be used.
Example: res can now be used and tests still pass.

* Forgot the \ in front of )

curriculum/challenges/english/04-data-visualization/json-apis-and-ajax/get-json-with-the-javascript-fetch-method.md

@@ -49,7 +49,7 @@ Your code should use `then` to convert the response to JSON.
 ```js
 assert(
   code.match(
-    /\.then\s*\(\s*(response|\(\s*response\s*\))\s*=>\s*response\s*\.json\s*\(\s*\)\s*\)/g
+    /\.then\s*\(\s*\(?(?<var>\w+)\)?\s*=>\s*\k<var>\s*\.json\s*\(\s*\)\s*\)/g
   )
 );
 ```