Try to fix issue with actions build fail

[JakeRoggenbuck]

Description of the changes

Currently there is a dependency issue in the GitHub action. This PR is an attempt to address this issue.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Formal verification
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactorization (non-breaking change which improves code quality)

How to test this PR?

GitHub actions will run automatically

[orangecms]

Hi there, I had a quick look; the setup here relies on Python 2.7.
Python 2 has been deprecared long ago and finally been removed in Ubuntu 24.04, and you're using ubuntu-latest, which no longer has it.

Any chance to migrate to later tooling that no longer depends on it?
Otherwise, a venv would be a solution, requiring some more fiddling.

[orangecms]

I don't know if Python 2.7 can just be removed from the install list, have never worked with opam.
Suggesting to upgrade opam here and drop Python 2.7: #103

[orangecms]

figured that opam can just be installed from Ubuntu, see #103 :)

[wojciechozga]

Thanks for your PR. We fixed the dependency issue in #104 . We keep building opam from sources to maintain better control over its version. I close this PR since the problem has been fixed.