Type extension issue with `allows ref struct`

A type extension on Seq<'T> does not work. The compiler appears to expect 'T to be constrained but I do not know how.

The code below used to work in prior versions of .NET up until .NET 9.0.0-rc2. Starting with .NET 9.0.100 the code is broken. The new compiler breaks helper type extensions at the bottom of our software stack.

**Repro steps**

Provide the steps required to reproduce the problem:

1. Install .NET SDK 9.0.100
2. Create a F# library project targeting .NET 9
3. Use the following code in Library.fs:

```fsharp
module SeqExtensions

type System.Collections.Generic.IEnumerable<'T> with

member _.Foo = ()
```

**Expected behavior**

~~Compilation errors.~~

**Actual behavior**

Compilation errors:

* Library.fs(3, 6): [FS0957] One or more of the declared type parameters for this type extension have a missing or wrong type constraint not matching the original type constraints on 'IEnumerable<_>'
* Library.fs(3, 45): [FS0341] The signature and implementation are not compatible because the type parameter 'T' has a constraint of the form 'T: allows ref struct but the implementation does not. Either remove this constraint from the signature or add it to the implementation.

**Known workarounds**

* Not using type extensions
* Not using .NET 9 and F# 9