[test] list expected changes to MutableCollection

Author: glessard

test/api-digester/Outputs/stability-stdlib-source-x86_64.swift.expected

@@ -1,4 +1,7 @@
+Accessor MutableCollection.subscript(_:).Get() has generic signature change from <Self where Self : Swift.MutableCollection> to <Self where Self : Swift.MutableCollection, Self.SubSequence == Swift.Slice<Self>>
+Accessor MutableCollection.subscript(_:).Set() has generic signature change from <Self where Self : Swift.MutableCollection> to <Self where Self : Swift.MutableCollection, Self.SubSequence == Swift.Slice<Self>>
 Protocol CodingKey has added inherited protocol Sendable
 Protocol CodingKey has generic signature change from <Self : Swift.CustomDebugStringConvertible, Self : Swift.CustomStringConvertible> to <Self : Swift.CustomDebugStringConvertible, Self : Swift.CustomStringConvertible, Self : Swift.Sendable>
 Protocol Error has added inherited protocol Sendable
 Protocol Error has generic signature change from to <Self : Swift.Sendable>
+Subscript MutableCollection.subscript(_:) has generic signature change from <Self where Self : Swift.MutableCollection> to <Self where Self : Swift.MutableCollection, Self.SubSequence == Swift.Slice<Self>>