Add exception for height and width for SkeletonBox in no-system-props rule (#389)

* Update no-system-props rule for SkeletonBox

Author: llastflowers

.changeset/chatty-penguins-breathe.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-primer-react": patch
+---
+
+Add exception for height and width for SkeletonBox in no-system-props rule

src/rules/no-system-props.js

@@ -48,6 +48,7 @@ const excludedComponentProps = new Map([
   ['PointerBox', new Set(['bg'])],
   ['Truncate', new Set(['maxWidth'])],
   ['Stack', new Set(['padding', 'gap'])],
+  ['SkeletonBox', new Set(['width', 'height'])],
 ])
 
 const alwaysExcludedProps = new Set(['variant', 'size'])