Add ECMWF CDS and EarthData API keys to pytest-remote-data.yml

[kandersolar]

Similar to #1531, this makes new GitHub Secrets available to the pytest remote-data workflow. This must be done separately from the PRs that want to use the secrets (#2572, #2573) because (quoting #1497 (comment)):

I think it is just the annoying but secure behavior of pull-request-target not respecting yml changes in the PR -- your update to include the SA key in the environment isn't taking effect because the action is defined by the .github/workflows/pytest-remote-data.yml file on master, not this PR branch. I guess the cleanest workaround is to submit a separate PR to change pytest-remote-data.yml, merge that, then merge master into this PR?