CI: restore the CI_DESIRED_RUNTIME check

[Somay-kousis]

CI_DESIRED_RUNTIME was only set in .cirrus.yml, and that file went away with
3743b9f ("Goodbye Cirrus"). The tests that read it are still there though,
so right now both of these just skip on every run:

• test/e2e/info_test.go, "Podman info: check desired runtime"
• test/system/005-info.bats, "podman info - confirm desired runtime"

When the var is empty they check CIRRUS_CI as a fallback, and that's obviously
never set under GHA, so they always hit the skip and the die()/Fail() under it
is unreachable. So the check from #14912 hasn't actually run since we moved off
Cirrus.

You can see it with:

git show 3743b9f806^:.cirrus.yml | grep CI_DESIRED
grep -rn CI_DESIRED_RUNTIME --include=*.yml .

So I set the variable in runner.sh and switched both tests to check
GITHUB_ACTIONS instead.

Couple of things I'm not sure about:

I ended up touching ci.sh too. limactl shell doesn't pass the host env into the
VM, so GITHUB_ACTIONS never reaches the tests and they'd have kept skipping
anyway. Passing it in explicitly was the simplest thing I could come up with,
happy to change it if you'd do it some other way. Both vars are in
PRESERVE_ENVS for the same reason, otherwise sudo drops them in the rootful
jobs.

I also hardcoded crun instead of deriving it from OCI_RUNTIME. I did derive it
at first, then realised OCI_RUNTIME is what picks the runtime in the first
place, so the test would just be comparing the value against itself and could
never fail. .cirrus.yml hardcoded it too so I'm guessing that was the point.

Left CI_DESIRED_STORAGE alone even though it's broken the same way. .cirrus.yml
set it to composefs on rawhide but STORAGE_FS there is overlay, and I couldn't
work out which one .Store.GraphDriverName is supposed to match. Can do it as a
follow up, or in here if you tell me which is right.

make validatepr passes. The real test is CI though, the desired runtime tests
should actually run now instead of skipping.

[Somay-kousis]

Closing, I found #29301 after opening this. Same files and it's further along. I also had this keyed off GITHUB_ACTIONS, which @Luap99 already pointed out over there is a poor marker since anyone running the tests in their own fork gets it set. PODMAN_CI in runner.sh is the better one.