docs(react): Fix typo in Grid.mdx (#11584)

Fixes a typo in the React Grid component docs.

Co-authored-by: Josh Black <[email protected]>

packages/react/src/components/Grid/Grid.mdx

@@ -143,7 +143,7 @@ In these situations, you can make use of the auto columns feature of the
 breakpoint props, and it will automatically set each column to a percentage of
 the total available width.
 
-For example, if you have on `Column` component it would span 100%, two `Column`
+For example, if you have one `Column` component it would span 100%, two `Column`
 components would span 50% each, four `Column` components would span 25% each,
 and so on.