Custom schema loader Typescript error "Cannot use import statement outside a module"

### Which packages are impacted by your issue?

_No response_

### Describe the bug

I'm trying to generate react hooks for the next.js application with codegen custom schema loader.
It looks like the codegen get an error `Cannot use import statement outside a module` while trying to get default export from ts file.

customLoader.ts:

```
import { makeSchema } from "nexus";
import * as casesTypes from "./cases";

const schema = (schemaString: string, config: any) => {
return makeSchema({
types: [casesTypes],
});
};

export default schema;
```

tsconfig.json:

```
{
"compilerOptions": {
"target": "ES5",
"module": "ESNext",
"lib": ["dom", "dom.iterable", "esnext"],
"allowJs": true,
"skipLibCheck": true,
"strict": true,
"forceConsistentCasingInFileNames": true,
"noEmit": true,
"esModuleInterop": true,
"moduleResolution": "node",
"resolveJsonModule": true,
"isolatedModules": true,
"jsx": "preserve",
"incremental": true,
"plugins": [
{
"name": "next"
}
],
"paths": {
"@/*": ["./src/*"],
"@api": ["./src/app/api"]
}
},
"include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
"exclude": ["node_modules"]
}
```

running script:

```
"generate": "graphql-codegen-esm --config codegen.json"
```

I hope that it's not a bug and I just did something wrong, but I've tried to follow the guidelines.

### Your Example Website or App

https://the-guild.dev/graphql/codegen/docs/config-reference/schema-field#custom-schema-loader

### Steps to Reproduce the Bug or Issue

1. create simple next js app
2. add nexus and prisma
3. use provided configuration files
4. run `yarn generate`

### Expected behavior

As a user, I expected custom loader is running, but it's have `SyntaxError: Cannot use import statement outside a module` error

### Screenshots or Videos

_No response_

### Platform

- OS: macOS
- NodeJS: v18.13.0
- "next": "13.4.12"
- "prisma": "^5.0.0"
- "nexus": "^1.3.0"
- "@graphql-codegen/cli": "5.0.0"
- "typescript": "4.9.5"

### Codegen Config File

{
"emitLegacyCommonJSImports": false,

"schema": {
"localnexusapi": {
"loader": "./src/graphql/customLoader.ts"
}
},
"documents": "./src/graphql/**/*.graphql",
"overwrite": true,
"generates": {
"./src/api/index.tsx": {
"plugins": [
"typescript",
"typescript-operations",
"typescript-react-apollo"
],
"config": {
"maybeValue": "T | undefined",
"withHooks": true
}
}
}
}

### Additional context

I've already tried guides:

https://the-guild.dev/graphql/codegen/docs/getting-started/esm-typescript-usage (change tsconfig and package.json type prop)

and

https://the-guild.dev/graphql/codegen/docs/config-reference/schema-field#custom-schema-loader (to return function by default to return generated schema object from nexus)