PRs from forked branches can't run CI tests

[jrhender]

Because PRs from repo forks don't have access to GitHub secrets (see GHA docs), PRs from forked repos won't be able to pass the CI currently. This is because the pr-check CI job currently includes a step of updating the cached Coda data for tests (i.e. npm run refresh-test-data) which involves making requests to Coda, which requires the Coda authorization token. This was experienced here.

This isse was discussed on Discord here.
Proposed solution options are:

1. Remove redownloading from GH PR check action and make a separate GH action for updating cached test data (only for manual run. This could be similar to this previous GH action that was used to commit new versions of data for semantic search
2. Host the test cache externally (so as to remove the cache remove being directly in the repo). This is what is currently done to fetch semantic search data (fetch('https://storage.googleapis.com/stampy-nlp-resources/stampy-encodings.json') in tfWorker.js)

[jrhender]

I plan on implementing the first solution as it is less effort than the second solution, in my opinion.

[jrhender]

This is complete from PR #354