While preparing my latest series, I noticed that the GitHub Actions CI
builds were cancelling the 'static-analysis' job because of a brownout of
Ubuntu 18.04. We are recommended to upgrade to 20.04.

However, we explicitly chose 18.04 in d051ed77ee6
(.github/workflows/main.yml: run static-analysis on bionic, 2021-02-08)
because coccinelle was not available in 20.04. It still isn't available
since I tried the basic update and it failed [1]

[1] https://github.com/gitgitgadget/git/runs/7955077955?check_suite_focus=true#step:3:98

Does anyone have an idea of how to install coccinelle on this newer
version? Should we try compiling it from source for this job? Should we
consider moving off of coccinelle and onto a different tool?

Thanks,
-Stolee