Improve concurrency of build processes on AIX machines.

Many of our current AIX machines have significant processing power and RAM (Most are 4-core with SMT8) and 32GiB if RAM. We are currently throttling some of them to -j8 or lower which means the machines are likely to be underutilised relative to their ability:

https://github.com/nodejs/build/blob/7d8af5b858e3e6b22b198e4091a09ecc32bc7cb2/ansible/inventory.yml#L122

This issue will cover experimenting to see if we can increase this, as duering some recent testing I have been running directly on the machine with values of -j16 without issues (Noting that it's also possible that running through jenkins has different effects...)

The limitations were initially put in due to the analysis in https://github.com/nodejs/build/issues/2566 and then added to our automation in https://github.com/nodejs/build/pull/2574 - it's not clear which versions of Node were affected but I will also try node.js 22 to cover both ends of what we are supporting. I will also note that the specific machine which was listed as failing with anything greater than 3 is currently offline.

Start with ansible/inventory.yml at the referenced AIX machine entry, then review the analysis in issue #2566 and automation changes from pull request #2574. Compare direct and Jenkins-driven builds at higher concurrency using the supported Node.js versions, including Node.js 22. Done means establishing a safe AIX concurrency setting and applying it to the build automation if testing supports the change.