Merge pull request #2735 from ahoppen/6.0/formatmode-sendable

[6.0] Mark `FormatMode` as `Sendable`

Author: ahoppen

Sources/SwiftSyntaxMacros/MacroProtocols/Macro+Format.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Describes the mode to use to format the result of an expansion.
-public enum FormatMode {
+public enum FormatMode: Sendable {
   /// Perform a basic format of the expansion. This is primarily for inserting
   /// whitespace as required (eg. between two keywords), but also adds simple
   /// newline and indentation.