grafana/toolkit: Fix failing linter when there were lint issues (#21849)

packages/grafana-toolkit/src/cli/tasks/plugin.build.ts

@@ -149,7 +149,9 @@ export const lintPlugin = useSpinner<Fixable>('Linting', async ({ fix }) => {
 
 
   if (lintResults.length > 0) {
   if (lintResults.length > 0) {
     console.log('\n');
     console.log('\n');
-    const failures: RuleFailure[] = lintResults.flat();
+    const failures = lintResults.reduce<RuleFailure[]>((failures, result) => {
+      return [...failures, ...result.failures];
+    }, []);
     failures.forEach(f => {
     failures.forEach(f => {
       // tslint:disable-next-line
       // tslint:disable-next-line
       console.log(
       console.log(