Update ESLint rule tests for flat config format

- Update RuleTester to use flat config languageOptions instead of
  eslintrc parser format
- Remove duplicate test case that ESLint v9 now detects
- Add Jest globals for test files

eslint.config.mjs

@@ -210,4 +210,14 @@ export default tseslint.config(
       'no-control-regex': 'off',
     },
   },
+
+  // Test files configuration
+  {
+    files: ['**/__tests__/**/*.{js,jsx,ts,tsx}', '**/*.test.{js,jsx,ts,tsx}'],
+    languageOptions: {
+      globals: {
+        ...globals.jest,
+      },
+    },
+  },
 )