Variational Embedding CI compatibility.

[cjcscott]

Despite merging #118 , pygnme is still not playing nicely with the CI and so the tests aren't being run automatically. This could lead to issues down the road, so I'm putting this here to flag that this is the case.

[maxnus]

Hi Charlie, as far as I can tell, on #118 you do not request pygnme for the CI build: https://github.com/BoothGroup/Vayesta/pull/118/files#diff-944291df2c9c06359d37cc8833d182d705c9e8c3108e7cfe132d61a06e9133ddR38

[cjcscott]

pygnme doesn't work with the CI so requesting it leads to all runs failing. Many of the commits on that PR are valiant but unsuccessful attempts by @abhishekkhedkar09 to get a working configuration, which we deleted before merger to avoid crashing everything.

[abhishekkhedkar09]

Even after plenty of trial-and-errors, I could not get pygnme to install on CI. Its dependencies are not set! At that time we chose to keep it as an optional dep.