Address review comments

Author: asl

CodeGeneration/Sources/SyntaxSupport/AttributeNodes.swift

@@ -385,7 +385,7 @@ public let ATTRIBUTE_NODES: [Node] = [
       ),
       Child(
         name: "accessorSpecifier",
-        kind: .token(choices: [.keyword(.get), .keyword(.set)]),
+        kind: .token(choices: [.keyword(.get), .keyword(.set), .keyword(._modify)]),
         documentation: "The accessor name.",
         isOptional: true
       ),

Sources/SwiftParser/Attributes.swift

@@ -650,7 +650,8 @@ extension Parser {
     let unexpectedBeforeAccessor: RawUnexpectedNodesSyntax?
     let accessor: RawTokenSyntax?
     if period != nil {
-      (unexpectedBeforeAccessor, accessor) = self.expect(.keyword(.get), .keyword(.set), .keyword(._modify), default: .keyword(.get))
+      (unexpectedBeforeAccessor, accessor) = self.expect(.keyword(.get), .keyword(.set), .keyword(._modify),
+                                                         default: .keyword(.get))
     } else {
       (unexpectedBeforeAccessor, accessor) = (nil, nil)
     }