* ci: try nix-community/cache-nix-action
* ci: add cache-id param to setup-nix action
* ci: tidy up cache keys for non-nix jobs
* ci: merge-nix-caches-linux job
* ci: merge caches other way around
* ci: reduce number of caches
Should prevent disk overflow
* ci: change cache id prefix for merge
* ci: comment out cache merging job
* ci: revert cache id prefix
* ci: setup-nix: use latest cache-nix-action
Among others, makes action logs look more tidy (see https://github.com/nix-community/cache-nix-action/commit/17d19d3d8be918757589635bc1a6830be0b129d2)
* ci: use test-pg cache key for loadtest
