[Diagnostics] Adjust brittle diagnostic to be insensitive to the specific mismatched type (see swiftlang#36267)

Author: xwu

test/Constraints/generics.swift

@@ -648,7 +648,7 @@ let arr = [BottleLayout]()
 let layout = BottleLayout(count:1)
 let ix = arr.firstIndex(of:layout) // expected-error {{referencing instance method 'firstIndex(of:)' on 'Collection' requires that 'BottleLayout' conform to 'Equatable'}}
 
-let _: () -> UInt8 = { .init("a" as Unicode.Scalar) } // expected-error {{initializer 'init(_:)' requires that 'Unicode.Scalar' conform to 'BinaryInteger'}}
+let _: () -> UInt8 = { .init("a" as Unicode.Scalar) } // expected-error {{initializer 'init(_:)' requires that 'Unicode.Scalar' conform to }}
 
 // https://bugs.swift.org/browse/SR-9068
 func compare<C: Collection, Key: Hashable, Value: Equatable>(c: C)