test: insert trailing newline in files generated with --save-actual-as-expected

The proper formatting is done by prettier via husky, but this part is easy to fix

Author: Yogu

spec/regression/regression-suite.ts

@@ -406,7 +406,11 @@ export class RegressionSuite {
         }
 
         if (this.options.saveActualAsExpected && !deepEqual(actualResult, expectedResult)) {
-            writeFileSync(resultPath, JSON.stringify(actualResult, undefined, '  '), 'utf-8');
+            writeFileSync(
+                resultPath,
+                formatWhitespaceInFile(JSON.stringify(actualResult, undefined, '  ')),
+                'utf-8',
+            );
         }
 
         return {