prevent external deprecations from failing CI tests

[jrushlow]

• silence external deprecation notices in CI
• add CI build that is allowed to fail to catch all deprecation notices

refs #85

[kbond]

Too bad github actions doesn't have an "allow failure" option for a workflow. At least we are still able to see the deprecation warnings in the job output.

I think as long as we are testing dev-master, we would start to see tests fail once the deprecated code is removed. Using a cron build trigger could help if there is a large amount of time between contributions.

[jrushlow]

I have a couple ideas about how to trigger "allowed failures" from indirect deprecation notices, but those are outside the scope of this PR.

In the meantime, will merge to fix current CI and look into the above separately.