Release: do not fail when mastodon auth fails

Release: make sure release artefacts are present for the tagging job

Add a workflow for easily creating releases (#4952)

I humbly present a solution our lack of releases: a workflow that can be
triggered to automatically create one. This workflow builds the project,
creates a GitHub release, and publishes beets to PyPi, for a one-stop
solution.

@sampsyo this would make it much easier to create releases, as it
requires only one little interaction: going to the actions tab and
entering a version number. Once that's done, the workflow should take
care of the rest.

I have only tested the `build` job so far, since I can't do anything
about the pypi or do a release just to test, but the code is lifted from
other similar actions and should work fine.

It also requires one piece of setup. This is that PyPi must be set up
with a [trusted publisher](https://docs.pypi.org/trusted-publishers/) to
receive the new package. Once that's done, the process should go off
automatically.

Release date for v1.5.0

Release date for 1.4.9

Travis: temporarily disable Python 3.8

There seems to be a compatibility error in Werkzeug on the prerelease of
3.8.

Don't require python2 for releases

Release date for 1.4.6

Add date to changelog