[BUG]: Custom schema migrations are not working

### Duplicate of [this issue](https://github.com/drizzle-team/drizzle-orm/issues/1592). Accidentally pushed it to the wrong repo.

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

0.29.1

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

0.20.6

### Describe the Bug

I am new to drizzle. I tried to create tables in separate, custom schema, using the examples from official [github](https://github.com/drizzle-team/drizzle-orm/tree/main/examples/pg-proxy) and custom schema usage from [official documentation](https://orm.drizzle.team/docs/schemas). Generation of the schema works fine but when I try to migrate a postgres database I get:
```bash
npm run migrate

> pg-proxy@1.0.0 migrate
> drizzle-kit push:pg

drizzle-kit: v0.20.6
drizzle-orm: v0.29.1

No config path provided, using default path
Reading config file '/Users//repos/opensource/pg-proxy/drizzle.config.ts'
[i] No changes detected
```

Schema is:
`schema.ts`
```ts
import { pgSchema, serial, text } from "drizzle-orm/pg-core";

const mySchema = pgSchema('test');

export const users = mySchema.table("users", {
id: serial("id").primaryKey(),
name: text("name").notNull(),
email: text("email").notNull(),
cityId: serial("city_id").references(() => cities.id),
});

export const cities = mySchema.table("cities", {
id: serial("id").primaryKey(),
name: text("name").notNull(),
});
```
Notice that the database is empty, just created using docker-compose. The `drizzle-kit generate:pg --schema src/schema.ts` command produces following schemas:
`0000_futuristic_devos.sql`
```sql
CREATE TABLE IF NOT EXISTS "test"."cities" (
"id" serial PRIMARY KEY NOT NULL,
"name" text NOT NULL
);
--> statement-breakpoint
CREATE TABLE IF NOT EXISTS "test"."users" (
"id" serial PRIMARY KEY NOT NULL,
"name" text NOT NULL,
"email" text NOT NULL,
"city_id" serial NOT NULL
);
--> statement-breakpoint
DO $$ BEGIN
ALTER TABLE "test"."users" ADD CONSTRAINT "users_city_id_cities_id_fk" FOREIGN KEY ("city_id") REFERENCES "test"."cities"("id") ON DELETE no action ON UPDATE no action;
EXCEPTION
WHEN duplicate_object THEN null;
END $$;
```
Notice how the produced SQL does not have any schema-related creations. it just tries to create a table in the `test` schema.
It is strange why does `generate` command does not create a `test` schema first and only then creates tables inside of this schema. Maybe this is an expected behaviour and custom schema should be created beforehand in a separate schema or something?
If I change `schema.ts` to this:
`schema.ts`
```ts
import { pgTable, serial, text } from "drizzle-orm/pg-core";

export const users = pgTable("users", {
id: serial("id").primaryKey(),
name: text("name").notNull(),
email: text("email").notNull(),
cityId: serial("city_id").references(() => cities.id),
});

export const cities = pgTable("cities", {
id: serial("id").primaryKey(),
name: text("name").notNull(),
});
```
Then delete migration files, regenerate them and migrate everything works as expected and migrations are applied.

### Expected behavior

I expect `drizzle-kit push:pg` command to create a custom schema, tables inside this schema or at least tell me what is the issue and why after running this command I don't see any changes in the DB.

### Environment & setup

Hardware: MacBook Pro (m1)
System Version: macOS 14.1.1 (23B81)
Postgres version: 15.5
Runtime: npm 9.8.1, node v18.18.2

`drizzle.config.ts`
```ts
import { defineConfig, type Config } from "drizzle-kit";
require("dotenv").config();

// DB_URL is postgres://postgres:postgres@localhost:5431/bug?search_path=test
export default defineConfig({
schema: "src/schema.ts",
out: "drizzle",
driver: "pg",
dbCredentials: {
connectionString: process.env["DB_URL"]!,
},
verbose: true,
strict: true,
}) satisfies Config;
```