fix(actions): try to recover if just fails to install

[ledif]

Related to ublue-os/bluefin#2106.

Lately, there are some flaky failures for jobs while installing just. For example, in the past few days, the following jobs to build images have failed:

• https://github.com/ublue-os/aurora/actions/runs/12607607121/job/35139162573
• https://github.com/ublue-os/aurora/actions/runs/12577208839/job/35054350351

The command curl -L https://api.github.com/repos/casey/just/releases/latest | jq -r '.tag_name' is sometimes returning "null" instead of an actual version, but it's difficult to tell if the curl call is failing or if it's returning a payload that is being parsed incorrectly.

In either case, adding --retry to curl and if it's still null, hardcoding a known good version should do the trick for now.

[m2Giles]

Something like this would be a bit more resistant

          while [[ "${JUST_VERSION:-}" =~ null || -z "${JUST_VERSION:-}" ]]
          do
            JUST_VERSION=$(curl -L https://api.github.com/repos/casey/just/releases/latest | jq -r '.tag_name')
          done

[ledif]

I updated the PR based on suggestions. Could I get a re-approval please? :)