Don't export GraphQLClientRequestHeaders in src/index.ts

[janhlavin]

Description

I can't use import { GraphQLClientRequestHeaders } from "graphql-request", because I get error: TS2614: Module '"graphql-request"' has no exported member 'GraphQLClientRequestHeaders'

type GraphQLClientRequestHeaders doesn't export in src/index.ts

Reproduction Steps/Repo Link

I configure project by Pure ESM package:

• in package.json

{
  "type": "module",
  "engines": [
    "node": ">=16"
  ],
  "dependecies": {
    "graphql-request": "^6.1.0"
  }
}

• in tsconfig.json

{
  "compilerOptions": {
    "module": "node16",
    "moduleResolution": "node16"
  }
}

[jonkoops]

This has been fixed under #616