This further reduces our usage of cache storage by caching the metadata
only once per repo. Now the metadata cache is ~250MB and the individual
caches with built dependencies are ~10M each.
Related: cfe99998fc
Related: https://github.com/xmonad/X11/pull/75
Stack installation of GHC takes more than a gigabyte, so caching it
wastes space (GitHub docs say it will be aggressively evicted after
reaching the 5G limit) and also time (compression, decompression).
Related: 9fce3805fc
Related: a5cee9bac2
Related: https://github.com/xmonad/X11/pull/75
Drop nightly and lts-15: they don't add GHC versions to the matrix and
new deps are better tested in the haskell-ci (cabal) workflow.
There's also little point in testing against both xmonad 0.15 and xmonad
master with all LTS versions. Drop most of those, reduces GitHub cache
and CPU time usage.
Related: fd243ca1c1
Related: https://github.com/xmonad/X11/pull/75