fix: add optional chaining before access to the targetRevision field (argoproj#23397)

Signed-off-by: daengdaengLee <[email protected]>
Signed-off-by: enneitex <[email protected]>

Author: daengdaengLee

ui/src/app/applications/components/applications-list/applications-labels.tsx

@@ -8,7 +8,7 @@ import './applications-labels.scss';
 export const ApplicationsLabels = ({app}: {app: Application}) => {
     const labels = (
         <>
-            <span className='application-labels__item'>{getAppDefaultSource(app).targetRevision || 'HEAD'}</span>
+            <span className='application-labels__item'>{getAppDefaultSource(app)?.targetRevision || 'HEAD'}</span>
             {Object.keys(app.metadata.labels || {}).map(label => (
                 <span className='application-labels__item' key={label}>{`${label}=${app.metadata.labels[label]}`}</span>
             ))}