test: default to assuming source is a script rather than a module

Author: G-Rath

tests/src/rule-tester.js

@@ -9,7 +9,7 @@ export function withoutAutofixOutput(test) {
 }
 
 export class FlatCompatRuleTester {
-  constructor(testerConfig) {
+  constructor(testerConfig = { parserOptions: { sourceType: 'script' } }) {
     this._tester = new RuleTester(FlatCompatRuleTester._flatCompat(testerConfig));
   }