message: PageLayout: Fix containerWidth default value in docs
  The default value for the `containerWidth` prop is `xlarge`, but the docs incorrectly say it's `full`.
diff: @@ -158,7 +158,7 @@ See [storybook](https://primer.style/react/storybook?path=/story/layout-pagelayo
  | 'medium'
  | 'large'
  | 'xlarge'`}
  - defaultValue="'full'"
  + defaultValue="'xlarge'"
  description="The maximum width of the page container."
  />
  <PropsTableRow
  