fix(#7022): remove ProgressBar artifacts from Notifications (#7024)

* fix: check for null or undefined

* refactor: `lint:fix`

---------

Co-authored-by: Scott Bell <scott@traclabs.com>

src/ui/layout/status-bar/NotificationBanner.vue

@@ -40,7 +40,7 @@
     >
 
     <progress-bar
-      v-if="activeModel.progressPerc !== null"
+      v-if="activeModel.progressPerc"
       class="c-message-banner__progress-bar"
       :model="activeModel"
     />
@@ -178,7 +178,7 @@ export default {
         return;
       }
 
-      if (this.activeModel.progressPerc !== null) {
+      if (this.activeModel.progressPerc) {
         maximizedDialog = this.openmct.overlays.progressDialog({
           buttons: [minimizeButton],
           ...this.activeModel