[Issue 20670] immutable template specialization pattern matches immutable struct, strips immutable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20670

--- Comment #15 from Dennis <dkorpel at live.nl> ---
(In reply to FeepingCreature from comment #13)
> This is how we want every struct in the domain layer to look.

Would this work?
```
struct S {
    immutable:
    // fields...
}
```

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