Add a flag to the transcript tests to use the new runtime
Add a flag to the transcript tests to use the new runtime

- The new runtime should pass the existing transcripts, so this was an
  oversight. Running this test with `--new-runtime` would previously
  just do an identical set of tests, using the old runtime for most
  transcripts and the new runtime only for things in the specific new
  runtime directory.

unisonweb/platform,unisonweb/platform,unisonweb/platform