[BUG]: Cannot specify schema.ts when introspecting. we want to use _schema.ts instead of schema.ts

### What version of `drizzle-orm` are you using?

0.30.1

### What version of `drizzle-kit` are you using?

0.20.14

### Describe the Bug

We have following config

``` js
import * as dotenv from "dotenv";
dotenv.config();

export default {
schema: "src/database/drizzle/_schema.ts",
out: "src/database/drizzle",
driver: "pg",
dbCredentials: {
user: process.env.DATABASE_USER,
password: process.env.DATABASE_PASSWORD,
host: process.env.DATABASE_HOST,
port: (process.env.DATABASE_PORT as any) as number,
database: process.env.DATABASE_NAME,
}
};```

the package.json scrpt looks like this:

"drizzle:migration:introspect": "drizzle-kit introspect:pg --config=src/database/ormconfigs/drizzlekit-config.ts"

Whenever we run the script the schema is generated in schema.ts and not _schema.ts. How to generate in _schema.ts instead ?

### Expected behavior

the introspected schema should be generated in _schema instead of schema.ts

### Environment & setup

Linux/Ubuntu 23.04, Xorg