ci: update 'static-analysis' to Ubuntu 22.04

ci: update 'static-analysis' to Ubuntu 22.04

GitHub Actions scheduled a brownout of Ubuntu 18.04, which canceled all
runs of the 'static-analysis' job in our CI runs. Update to 22.04 to
avoid this as the brownout later turns into a complete deprecation.

The use of 18.04 was set in d051ed77ee6 (.github/workflows/main.yml: run
static-analysis on bionic, 2021-02-08) due to the lack of Coccinelle
being available on 20.04 (which continues today).

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>