Use vcr for testing

[trangdata]

We currently make a few API requests to OpenAlex for testing in our GH Actions, which is triggered by each commit to a PR. A more graceful way to test would be to use vcr to "record" the cassettes of the responses and have one scheduled workflow once a week using real requests.

https://books.ropensci.org/http-testing/vcr.html

[maelle]

or hpttest. if you use httptest and then switch from httr to httr2, the switch from httptest to httptest2 is not too complicated (I had the experience of doing this myself this week: cynkra/fledge#646)

https://books.ropensci.org/http-testing/httptest.html