Merge pull request swiftlang#1360 from hborla/conformance-macro-fix

[Macros] Correct the where clause syntax type in `ConformanceMacro`.

Author: hborla

Sources/SwiftSyntaxMacros/MacroProtocols/ConformanceMacro.swift

@@ -32,5 +32,5 @@ public protocol ConformanceMacro: AttachedMacro {
     of node: AttributeSyntax,
     providingConformancesOf declaration: Declaration,
     in context: Context
-  ) throws -> [(TypeSyntax, WhereClauseSyntax?)]
+  ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)]
 }