Switch to opam 2.2

[hhugo]

and native windows setup, instead of cygwin.

With this PR, the longest jobs (Windows ones) run in 3mins when using caches.

Blockers:

• fix gmp in opam (see Add configuration for gmp under mingw opam-repository#26102)
• wait for a v3 release of setup-ocaml

[hhugo]

I think the CI is broken because of the cache.
The CI is green in hhugo#3.
Can someone with enough permission clear the github action cache ?

[smorimoto]

Someone can use these to blow it up all at once.

• https://cli.github.com
• https://github.com/actions/gh-actions-cache

gh actions-cache list -L 100 | cut -f 1 | xargs -I CACHE_KEY gh actions-cache delete CACHE_KEY --confirm

[hhugo]

Someone can use these to blow it up all at once.

• https://cli.github.com
• https://github.com/actions/gh-actions-cache

gh actions-cache list -L 100 | cut -f 1 | xargs -I CACHE_KEY gh actions-cache delete CACHE_KEY --confirm

Or just

gh cache delete  --all

[antoinemine]

Or just

gh cache delete  --all

Done!

[hhugo]

@antoinemine, can you also stop the running jobs ?

[antoinemine]

@antoinemine, can you also stop the running jobs ?

Done!

[hhugo]

The issue should be fixed with ocaml/opam#6046 and a new release of opam 2.2

[hhugo]

This is now ready for review. CI is happy.

[hhugo]

Gentle ping

[xavierleroy]

OK, let's see how it works!