DEV: Work around a Docker issue (#13368)

Fixes our backend spec suite in GitHub Actions CI. For more information about the Docker issue see: https://github.com/docker/for-linux/issues/1015

(It's possible that error could also happen in dev/production, though thankfully that hasn't happened yet afaik)

lib/freedom_patches/copy_file.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require "fileutils"
+
+# See: https://github.com/docker/for-linux/issues/1015
+
+module FileUtils
+  class Entry_
+    def copy_file(dest)
+      File.open(path()) do |s|
+        File.open(dest, "wb", s.stat.mode) do |f|
+          IO.copy_stream(s, f)
+          f.chmod(f.lstat.mode)
+        end
+      end
+    end
+  end
+end