orm: allow using connections, that were explicitly casted to orm.Connection too (#17427)

vlib/orm/orm_interface_test.v

@@ -0,0 +1,31 @@
+import db.sqlite
+import orm
+
+struct User {
+	id   int    [primary; sql: serial]
+	name string
+}
+
+fn test_orm_interface() {
+	sqlite_db := sqlite.connect(':memory:') or { panic(err) }
+	db := orm.Connection(sqlite_db)
+
+	sql db {
+		create table User
+	}
+
+	user := User{
+		name: 'test'
+	}
+
+	sql db {
+		insert user into User
+	}
+
+	users := sql db {
+		select from User
+	}
+
+	assert users.len == 1
+	assert users.first().name == user.name
+}