Add some EasyCrypt integration test to the CI?

[erikmd]

As pointed out in PR https://github.com/ProofGeneral/PG/pull/501, it would be nice to add at least one integration test for EasyCrypt in the GitHub-actions based CI.

For the record, the two main files that handle this for Coq are:

• .github/workflows/test.yml

• ci/coq-tests.el

I'm not an EasyCrypt user so I guess I won't be able to quickly devise a proper configuration with GitHub Actions; but maybe @strub or one of the watchers of the PG repo would be interested and have the time to look at this?

Finally regarding the elisp test code itself (including mocks), most of the coq-tests.el is generic and could be reused/renamed actually: I believe the only specific code to update would be (coq-test-init).