Add Sidebar to SplitPageLayout props set (#565)

* Add Sidebar to SplitPageLayout props set

* Add changeset for SplitPageLayout.Sidebar update

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Marie Lucca <40550942+francinelucca@users.noreply.github.com>

Author: 3 people

.changeset/short-teeth-cheat.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-primer-react": patch
+---
+
+Add SplitPageLayout.Sidebar to no-system-props exclusions for padding, position, and width.

src/rules/no-system-props.js

@@ -34,6 +34,7 @@ const excludedComponentProps = new Map([
   ['SplitPageLayout.Footer', new Set(['padding'])],
   ['SplitPageLayout.Pane', new Set(['padding', 'position', 'width'])],
   ['SplitPageLayout.Content', new Set(['padding', 'width'])],
+  ['SplitPageLayout.Sidebar', new Set(['padding', 'position', 'width'])],
   ['StyledOcticon', new Set(['size'])],
   ['Octicon', new Set(['size', 'color'])],
   ['PointerBox', new Set(['bg'])],