Upsert doesn't work when there's unique index

Description

I've got the bug using PostgreSQL.

Create a table

$b->createTable('page', [
    'id' => $cb::uuidPrimaryKey(),
    'title' => $cb::string()->notNull(),
    'slug' => $cb::string()->notNull()->unique(),
    'text' => $cb::text()->notNull(),
    'created_at' => $cb::dateTime(),
    'updated_at' => $cb::dateTime(),
]);

Do upsert:

$this->connection->createCommand()->upsert('{{%page}}', [
    'id' => $page->id,
    'title' => $page->title,
    'slug' => $page->getSlug(),
    'text' => $page->text,
    'created_at' => $page->createdAt,
    'updated_at' => $page->updatedAt,
])->execute();

Get the error:

QLSTATE[42P10]: Invalid column reference: 7 ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification
The SQL being executed was: INSERT INTO "page" ("id", "title", "slug", "text", "created_at", "updated_at") VALUES ('019b5c77-1c8b-72bd-a0c9-547987f9cf9c', 'Test', 'test', 'test', '2025-12-26 21:01:08', '2025-12-26 21:01:08') ON CONFLICT ("id", "slug") DO UPDATE SET "title"=EXCLUDED."title", "text"=EXCLUDED."text", "created_at"=EXCLUDED."created_at", "updated_at"=EXCLUDED."updated_at"

Package version

2.0.0

PHP version

8.2

The relevant entry point is createCommand()->upsert(); start by reproducing the PostgreSQL example with the unique slug index and inspect how the ON CONFLICT specification is generated. Done means the shown schema can be upserted successfully without the invalid constraint error, with regression coverage for this case.