fix(mysql): use lenient flag comparison for ENUM types

[a4501150]

Summary

MySQL-compatible databases like TiDB may return ENUM columns with additional flags like NOT_NULL or NO_DEFAULT_VALUE. The previous exact flag comparison in MySqlTypeInfo::eq() caused type mismatches even though both sides were valid ENUM types.

This change makes ENUM comparison check only that both types have the ENUM flag set, ignoring other flags that don't affect type compatibility.

The Problem

When using #[derive(sqlx::Type)] on a Rust enum to decode from a MySQL ENUM column, decoding fails with:

mismatched types; Rust type `MyEnum` (as SQL type `ENUM`) is not compatible with SQL type `ENUM`

The issue is that MySqlTypeInfo::__enum() creates type info with only the ENUM flag (0x100), but the database may return columns with additional flags like NOT_NULL | ENUM (0x101). The strict equality check self.flags == other.flags fails.

The Fix

For ENUM types, only check that both sides have the ENUM flag set:

if self.flags.contains(ColumnFlags::ENUM) && other.flags.contains(ColumnFlags::ENUM) {
    return true;
}

Testing

• All existing sqlx-mysql tests pass
• Tested against TiDB Cloud with ENUM columns successfully

Fixes #3750
Refs #1241