fix(gatsby): add react-com as devDep

[jablko]

Add dev-dependency on @types/react-dom, missed in #22854 ❤️

yarn typecheck currently passes because node_modules contains @types/react-dom -- I think because gatsby-plugin-image already dev-depends on it? However packages/gatsby/index.d.ts depends on @types/react-dom since #22854.

My Gatsby project doesn't have an existing dependency on gatsby-plugin-image or @types/react-dom, so I get the following error when I typecheck my project:

$ npm test
node_modules/gatsby/index.d.ts:2:26 - error TS7016: Could not find a declaration file for module 'react-dom'.

2 import { Renderer } from "react-dom"
                           ~~~~~~~~~~~

Found 1 error.

This PR addresses that by adding the previously-undeclared dev-dependency.

[LekoArts]

Hi!

You'll need to run yarn at the root of the monorepo to also change the yarn.lock file.

[jablko]

@LekoArts Thanks! I've now added the yarn.lock file to this PR. ✔️

[LekoArts]

Thanks!