Fix TimelineItem--condensed background (#1556)

* Fix TimelineItem--condensed background

* Create silver-items-talk.md

Author: simurai

.changeset/silver-items-talk.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": patch
+---
+
+Fix TimelineItem--condensed background

src/timeline/timeline-item.scss

@@ -93,6 +93,7 @@
     // stylelint-disable-next-line primer/colors
     color: var(--color-icon-secondary);
     background-color: var(--color-bg-canvas);
+    background-image: none;
     border: 0;
   }
 }