"Enum Order is not backed" when value is not-int/string

Bug report

Although backed enum allows only int / string, PHPStan should warn for all types if the case value is assigned with any type. Currently there is no static analysis error.

Code snippet that reproduces the problem

https://phpstan.org/r/c628e80c-5511-4cfa-bded-7dbe9a7d216f

Expected output

PHPStan error for A - D case