[using-typescript] Fix typing in index layout component (#5969)
[using-typescript] Fix typing in index layout component (#5969)


mingaldrichgan/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,fk/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,0x80/gatsby,0x80/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,fk/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,fk/gatsby