Improve error handling of enums with query_as! macro

[HarrisonHemstreet]

Bug Description

When attempting to execute a SELECT query with the query_as! macro, the macro produces an error when the macro is used on a PostgreSQL table containing a column of type enum.

My understanding is that structs containing enums cannot be used with the query_as! macro and must instead be used with the query_as method. If this is the case a better error message containing something like, "cannot use query_as! macro with PostgreSQL custom types"

Minimal Reproduction

This gist is the main idea. You will have to add the proper imports and such, but the main idea is all here:
https://gist.github.com/HarrisonHemstreet/0d89f2a9bdd257d08a10b7e33c5600ae

use serde::{Deserialize, Serialize};

#[derive(sqlx::Type, Serialize, Deserialize, Debug)]
#[sqlx(type_name = "status", rename_all = "lowercase")]
pub enum Status {
    Active,
    Inactive,
    Suspended
}

#[derive(sqlx::FromRow, Serialize, Deserialize, Debug)]
pub struct TestEnum {
    pub id: Option<i32>,
    pub name: Option<String>,
    pub enum_col: Status,
}

            let returned: Result<TestEnum, Error> = sqlx::query_as!(
            TestEnum,
                r#"SELECT id, name, enum_col FROM test_enum LIMIT 1"#
            )
            .fetch_one(&pg)
            .await;


/*
PostgreSQL:
CREATE TYPE status AS ENUM ('active', 'inactive', 'suspended');

CREATE TABLE test_enum (
  id SERIAL PRIMARY KEY,
  name TEXT,
  enum_col status NOT NULL DEFAULT 'active'
);

insert into test_enum (name)  values ('test');
*/

/*
should produce this error:
```bash
error: unsupported type status of column #3 ("enum_col")
  --> src/routes/auth.rs:62:53
   |
62 |               let returned: Result<TestEnum, Error> = sqlx::query_as!(
   |  _____________________________________________________^
63 | |             TestEnum,
64 | |                 r#"SELECT id, name, enum_col FROM test_enum LIMIT 1"#
65 | |             )
   | |_____________^
   |
   = note: this error originates in the macro `$crate::sqlx_macros::expand_query` which comes from the expansion of the macro `sqlx::query_as` (in Nightly builds, run with -Z macro-backtrace for more info)
*/

Info

• SQLx version: 0.7.1
• SQLx features enabled: "postgres", "runtime-tokio", "chrono", "uuid", "macros"
• Database server and version: Postgres docker hub
• Operating system: ubuntu 22.04.3 LTS
• rustc --version: rustc 1.69.0 (84c898d65 2023-04-16)

[TmLev]

Have you seen this issue #1004?