The general skeleton of each job is the same, so consolidate the
definition to a single job with an explicit matrix.
Use conditional steps to handle steps that are unique to a certain job
(e.g., installing clang-11 for better ASAN support).
The env var is being set to the default value, as of ccache 3.3, which
is available in Zesty and newer. All of our CI is using Bionic, so this
is already available.
We have a GitHub Sponsors page for the neovim organization now:
- https://github.com/sponsors/neovim
It can be reached by clicking on the "Sponsor" button on the
[organization page](https://github.com/neovim).
This commit replaces Salt by GitHub Sponsors and Open Collective.
