Resolve remote testing on PRs

[mkelley]

As noted in #345 , we cannot use the NASA ADS API without publicly exposing a secret API key. These tests could be restored if the ads-based tests could be skipped (perhaps using a pytest.mark or a test that the key exists), or if the ads module was used in sandbox mode. Or may be use a combination of the two?

[jianyangli]

I thought you used the GitHub repository secret to save the ADS key and allow for tests using secret keys. Perhaps I missed something?

[mkelley]

Sorry, I mean for this to be specific to pull requests. We can indeed use the API key with our weekly tests.