fix(gatsby-plugin-react-helmet): Typo in onPreInit warning (#36419)

Author: alexlouden

packages/gatsby-plugin-react-helmet/src/gatsby-node.js

@@ -2,6 +2,6 @@ exports.pluginOptionsSchema = ({ Joi }) => Joi.object({})
 
 exports.onPreInit = ({ reporter }) => {
   reporter.warn(
-    `gatsby-plugin-react-helmet: Gatsby now has built-in support for modyfing the document head. Learn more at https://gatsby.dev/gatsby-head`
+    `gatsby-plugin-react-helmet: Gatsby now has built-in support for modifying the document head. Learn more at https://gatsby.dev/gatsby-head`
   )
 }