fix: Styles on Group example to be more consistent (#9071)

Author: snowystinger

packages/dev/s2-docs/pages/react-aria/Group.mdx

@@ -18,19 +18,19 @@ import {Input} from 'react-aria-components';
 
 <InputGroup/* PROPS */>
   <Input
-    size={3}
+    style={{width: '3ch', boxSizing: 'content-box'}}
     maxLength={3}
     aria-label="First 3 digits"
     placeholder="000" />
   –
   <Input
-    size={2}
+    style={{width: '2ch', boxSizing: 'content-box'}}
     maxLength={2}
     aria-label="Middle 2 digits"
     placeholder="00" />
   –
   <Input
-    size={4}
+    style={{width: '4ch', boxSizing: 'content-box'}}
     maxLength={4}
     aria-label="Last 4 digits"
     placeholder="0000" />