addToPath to prevent multiple param string starting chars (#19139)

.changelog/19139.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+ui: Fixed an issue where purging a job with a namespace did not process correctly
+```

ui/app/adapters/job.js

@@ -52,7 +52,12 @@ export default class JobAdapter extends WatchableNamespaceIDs {
   }
 
   purge(job) {
-    const url = this.urlForFindRecord(job.get('id'), 'job') + '?purge=true';
+    const url = addToPath(
+      this.urlForFindRecord(job.get('id'), 'job'),
+      '',
+      'purge=true'
+    );
+
     return this.ajax(url, 'DELETE');
   }