Fix "Run under bubblewrap" after forking

[reshi-reshlet]

Fix "Run under bubblewrap" after forking

"Run under bubblewrap" was failing after I forked the repo.
Here is what I did to fix it.

1. New Flex Mirror Links
   The original mirrors for flex-2.5.11 and flex-2.5.33 appear to be down.
   I replaced them with:

   • http://ftp-tel.sjtu.edu.cn/sites/ftp.openpkg.org/sources/DST/flex/flex-2.5.11.tar.gz
   • http://ftp-tel.sjtu.edu.cn/sites/ftp.openpkg.org/sources/DST/flex/flex-2.5.33.tar.gz

   The original mirror (http://download.nust.na/pub2/openpkg1) has been unreliable in the past.
   See:

   • Guix bootstrappable logs
     (search for "flex-2.5.11.tar.gz can't be download")
   • Failed build example

2. Ubuntu Version Check
   GitHub ran the workflow on Ubuntu 22.04.5 LTS,
   despite bwrap.yaml specifying runs-on: ubuntu-latest.
   This made the build fail when trying to do the AppArmor workaround.

   • See the failing build.
     you can see the ubuntu version in the "set up job" section.
   • Added a script to check the Ubuntu version,
     and apply the AppArmor workaround only if the version is >= 24.04.

3. Added Version Check Script to Lint Workflow
   New script clearing ShellCheck:

   • Lint workflow passing

4. Successful Workflow Execution
   "Run under bubblewrap" working in my fork:

   • Final working build

[fosslinux]

I'm not entirely sure this is the right way to go about it. I'd rather prefer that we change ubuntu-latest to ubuntu-24.04.

[reshi-reshlet]

Switching to ubuntu-24.04 would work. Seems nicer to have explicit deps anyway.
Thought I would whip up the 'version agnostic' fix, in case that would be preferred.

@fosslinux do you want me to adjust my branch? I am not the most familiar with doing pull requests, so if I was going to do this, I would maybe just make a new branch and submit a new PR (and close this one).

[fosslinux]

Yeah, you can do that, or otherwise the "usual" way of doing it would be to make the changes on this branch and just push the changes. But you can make a new PR if you would like.

[reshi-reshlet]

updated the branch: got rid of the version detection, and just switched to ubuntu-24.04

CI build started here (hasn't finished yet, but I expect it to 'work')
https://github.com/reshi-reshlet/live-bootstrap/actions/runs/12637879733