tempfork/registry: work around issue with Tailscale's redo build system

Updates tailscale/corp#293

tempfork/registry/fix_corp_redo_build_test.go

@@ -0,0 +1,8 @@
+package registry_test
+
+// Tailscale's redo-based build system doesn't know how to skip running Go tests
+// in directories that don't contain files for the current OS.
+//
+// https://github.com/tailscale/corp/issues/293
+//
+// So this is a dummy file for now to make it happy.