GitHub Action installs ElasticSearch before checking code style

[bencomp]

When I submitted #427 to fix the Flake8 errors that made an earlier build fail, I noticed that the current build workflow is set up to install ElasticSearch and other packages before checking the code style.

Perhaps "we" can save CI time by doing the light-weight code checking first, or even in parallel to other checks? And maybe caching dependencies can also save time, as well as using an ElasticSearch service container (though I have no experience with service containers).