Enable the unicorn/prefer-at ESLint plugin rule (PR 15008 follow-up)

Please find additional information here:
 - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at
 - https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/prefer-at.md

src/core/evaluator.js

@@ -3066,7 +3066,7 @@ class PartialEvaluator {
               }
             }
 
-            const item = elements[elements.length - 1];
+            const item = elements.at(-1);
             if (typeof item === "string") {
               showSpacedTextBuffer.push(item);
             }