Add a new path in sandbox for Xcode

When building a project which has SPM dependencies in Xcode, SPM will try and access (and potentially write in) `/Users/frizlab/Library/Caches/org.swift.swiftpm`.
I have added this path in the write exception for Xcode.

Library/Homebrew/sandbox.rb

@@ -74,6 +74,7 @@ class Sandbox
   # Xcode projects expect access to certain cache/archive dirs.
   def allow_write_xcode
     allow_write_path "#{Dir.home(ENV.fetch("USER"))}/Library/Developer"
+    allow_write_path "#{Dir.home(ENV.fetch("USER"))}/Library/Caches/org.swift.swiftpm"
   end
 
   def allow_write_log(formula)