unixPB: Add test devkit for riscv64 (GCC14.2/F28)

[sxa]

This will likely want to undergo a change to use a "production" devkit like the other Linux platforms instead of pulling from where it currently is, but this can be used for evaluation purposes in the meantime.

First step in a solution for #3637

Checklist

• commit message has one of the standard prefixes
• faq.md updated if appropriate
• other documentation is changed or added (if applicable)
• playbook changes run through VPC or QPC (if you have access) Working on it - the runs in https://ci.adoptium.net/view/Tooling/job/VagrantPlaybookCheck/2069 failed but none seem related to the devkit, so I don't believe this will cause any side effects.
• VPC/QPC not applicable for this PR
• for inventory.yml changes, bastillion/nagios/jenkins updated accordingly