Update for Swift 6.3

Author: colemancda

Package.swift

@@ -93,7 +93,11 @@ if buildDocs {
 
 if enableMacros {
     let version: Version
-    #if swift(>=6.1)
+    #if swift(>=6.3)
+    version = "603.0.1"
+    #elseif swift(>=6.2)
+    version = "602.0.0"
+    #elseif swift(>=6.1)
     version = "601.0.1"
     #else
     version = "600.0.1"