The POSIX compliance GitHub Actions workflow was overly complex, especially the ubuntu job and the security analysis job.
This change simplifies the workflow by:
- Removing manual cluster setup and teardown in the ubuntu job, relying on the Makefile instead. This makes the ubuntu job more consistent with the macos job.
- Simplifying the gosec installation in the security analysis job to use a single `go install` command.
- Removing complex scripting and fallbacks that made the workflow hard to read and maintain.