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

Author: hborla

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -752,7 +752,7 @@ func expandAttachedMacroInProcess(
       // the existential.
       func expandConformanceMacro<Node: DeclGroupSyntax>(
         _ node: Node
-      ) throws -> [(TypeSyntax, WhereClauseSyntax?)] {
+      ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)] {
         return try attachedMacro.expansion(
           of: sourceManager.detach(
             customAttrNode,

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1018,7 +1018,7 @@ public struct EquatableMacro: ConformanceMacro {
     of node: AttributeSyntax,
     providingConformancesOf decl: some DeclGroupSyntax,
     in context: some MacroExpansionContext
-  ) throws -> [(TypeSyntax, WhereClauseSyntax?)] {
+  ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)] {
     let protocolName: TypeSyntax = "Equatable"
     return [(protocolName, nil)]
   }