Move Cypress API version variables to workflow files

[danswick]

Our daily regression tests were failing due to environment variables set to outdated API version number (h/t @rnovak338). Those variables, CYPRESS_ADMIN_API_VERSION and CYPRESS_API_VERSION, are currently stored as repository secrets, which has a couple of downsides: as an individual, it's not possible to know the value of those variables; updating those variables requires elevated privileges and is a manual process.

Since these values aren't really secrets, it should be possible to set them in the regression test workflow configuration instead. Once we've moved the variables into workflow config, we'll need to delete the corresponding secrets to conduct a complete test.