ui: Fix a problem showing the default part in a non-primary (#11800)

When switching to a non-primary datacenter we should only show the word 'default' in place of the partition menu, this fixes up a bug preventing that from happening due to erroneous if/let nesting

ui/packages/consul-partitions/app/components/consul/partition/selector/index.hbs

@@ -1,8 +1,8 @@
 {{#if (can "use partitions")}}
-  {{#if (can "choose partitions" dc=@dc)}}
 {{#let
   (or @partition 'default')
 as |partition|}}
+  {{#if (can "choose partitions" dc=@dc)}}
       <li
         class="partitions"
         data-test-partition-menu
@@ -58,9 +58,9 @@ as |partition|}}
       class="partition"
       aria-label="Admin Partition"
     >
-      {{partition}}
+      {{'default'}}
     </li>
-{{/let}}
   {{/if}}
+{{/let}}
 {{/if}}