Revert "github actions: do not cache ~/.opam since we install in a local switch anyway". Commit contained a typo that causes Github Actions not to run at all. Also works without it.
Revert "github actions: do not cache ~/.opam since we install in a local switch anyway".
Commit contained a typo that causes Github Actions not to run at all. Also works without it.

This reverts commit dd94bbadeb7576df8848974b84767e827f83a6ec.

goblint/analyzer,goblint/analyzer,goblint/analyzer,goblint/analyzer,goblint/analyzer