fix: prevent progress bar flicker on app init (WPB-7378) (#17406)

Author: V-Gira

src/style/components/loading-bar.less

@@ -47,6 +47,7 @@
     var(--background-fade-8) 14px
   );
   background-size: @rotatedSize 4px;
+  margin-inline: auto;
 
   > div {
     width: 0;