Make it possible to add a colrv1 json test without altering a match

https://github.com/googlefonts/fontations/pull/817 broke the ability to add a test, run with an environment variable set to generate the master data, and then have your test work. Instead it will initially fail until a match statement is updated.

For context, cross-crate path building breaks in google3. A build.rs based approach, such as #816, should work but to date I haven't gotten that to function in google3.