(PA-8312) Skip gem source add for Solaris & AIX

[cthorn42]

After installing skip the gem source add part because we're running into memory issues and crashing. See PA-8312 for details.

[cthorn42]

Ad hoc job with this change passing: https://jenkins-platform.delivery.puppetlabs.net/view/puppet-agent/view/ad-hoc/job/platform_puppet-agent-extra_puppet-agent-integration-suite_adhoc-ad_hoc/1698/
And the output of the test from an AIX host:

12:29:48 Begin .bundle/gems/ruby/3.1.0/bundler/gems/beaker-puppet-1e3863dd9b95/setup/common/012_Finalize_Installs.rb
12:29:48 
12:29:48 Finalize Host Installation
12:29:48 
12:29:48 * Verify host times
12:29:48   
12:29:48   sole-asymmetry.delivery.puppetlabs.net (sole-asymmetry.delivery.puppetlabs.net) 19:29:48$ env PATH="/opt/puppetlabs/puppet/bin:${PATH}" ruby -e 'puts Time.now.strftime("%Y-%m-%d %T.%L %z")'
12:29:48     2026-03-12 12:29:48.315 -0700
12:29:48   
12:29:48   sole-asymmetry.delivery.puppetlabs.net (sole-asymmetry.delivery.puppetlabs.net) executed in 0.19 seconds
12:29:48   
12:29:48   aix72-1-pix.delivery.puppetlabs.net (aix72-1-pix.delivery.puppetlabs.net) 19:29:48$ env PATH="/opt/puppetlabs/puppet/bin:${PATH}" ruby -e 'puts Time.now.strftime("%Y-%m-%d %T.%L %z")'
12:29:48     2026-03-12 12:29:49.403 -0700
12:29:48   
12:29:48   aix72-1-pix.delivery.puppetlabs.net (aix72-1-pix.delivery.puppetlabs.net) executed in 0.17 seconds
12:29:48   Host times vary 1088 ms
12:29:48 
12:29:48 * Configure gem mirror
12:29:48   Skipping configure_gem_mirror for puppet9 on aix/solaris, issue with rubygems 4.0
12:29:48 Begin teardown
12:29:48 End teardown