error: 'Dog' does not implement protocol 'Speaker': method 'speak' has a mismatched signature — a protocol-method impl must not introduce its own type parameters (e.g. `$T: Type`); it must match the protocol's signature exactly
  --> examples/diagnostics/1198-diagnostics-protocol-erasure-generic-method.sx:20:3
   |
20 |   s : Speaker = d;   // <- 'Dog.speak' has a mismatched signature
   |   ^^^^^^^^^^^^^^^^