Improve progress-bar-stripes animation (#28697)

- `background-position: 0 0;` is the default background position, so redundant
- The background position should only be animated in the x direction
- `0%` is a little shorter than `from`

scss/_progress.scss

@@ -1,8 +1,7 @@
 // Disable animation if transitions are disabled
 @if $enable-transitions {
   @keyframes progress-bar-stripes {
-    from { background-position: $progress-height 0; }
-    to { background-position: 0 0; }
+    0% { background-position-x: $progress-height; }
   }
 }