Revert TimelineItem-badge fix (#1563)

* Revert `TimelineItem-badge` fix

* Create thirty-tips-help.md

Author: simurai

.changeset/thirty-tips-help.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": patch
+---
+
+Revert `TimelineItem-badge` fix

src/timeline/timeline-item.scss

@@ -34,8 +34,7 @@
   // stylelint-disable-next-line primer/colors
   color: var(--color-icon-secondary);
   align-items: center;
-  background-color: var(--color-bg-canvas); // covers the "line"
-  background-image: linear-gradient(0deg, var(--color-timeline-badge-bg), var(--color-timeline-badge-bg));
+  background-color: var(--color-timeline-badge-bg);
   // stylelint-disable-next-line primer/borders
   border: 2px $border-style var(--color-bg-canvas);
   border-radius: 50%;
@@ -93,7 +92,6 @@
     // stylelint-disable-next-line primer/colors
     color: var(--color-icon-secondary);
     background-color: var(--color-bg-canvas);
-    background-image: none;
     border: 0;
   }
 }