## Previously compiling example does not compile

The example in the testcase introduced in D1667 currently fails with,

```
ClassOperator.hs:12:3: error:
• Could not deduce (a ><> b0)
from the context: a ><> b
bound by the type signature for:
(**>) :: (a ><> b) => a -> a -> ()
at ClassOperator.hs:12:3-44
The type variable ‘b0’ is ambiguous
• In the ambiguity check for ‘**>’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
(**>) :: forall a b. (a ><> b) => a -> a -> ()
In the class declaration for ‘><>’
ClassOperator.hs:12:3: error:
• Could not deduce (a ><> b0)
from the context: a ><> b
bound by the type signature for:
(**<) :: (a ><> b) => a -> a -> ()
at ClassOperator.hs:12:3-44
The type variable ‘b0’ is ambiguous
• In the ambiguity check for ‘**<’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
(**<) :: forall a b. (a ><> b) => a -> a -> ()
In the class declaration for ‘><>’
ClassOperator.hs:12:3: error:
• Could not deduce (a ><> b0)
from the context: a ><> b
bound by the type signature for:
(>**) :: (a ><> b) => a -> a -> ()
at ClassOperator.hs:12:3-44
The type variable ‘b0’ is ambiguous
• In the ambiguity check for ‘>**’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
(>**) :: forall a b. (a ><> b) => a -> a -> ()
In the class declaration for ‘><>’
ClassOperator.hs:12:3: error:
• Could not deduce (a ><> b0)
from the context: a ><> b
bound by the type signature for:
(<**) :: (a ><> b) => a -> a -> ()
at ClassOperator.hs:12:3-44
The type variable ‘b0’ is ambiguous
• In the ambiguity check for ‘<**’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
(<**) :: forall a b. (a ><> b) => a -> a -> ()
In the class declaration for ‘><>’
```

This is a regression relative to 7.10.2, which accepts the program without error.

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