Replace defunct sles12 test node with sles15sp6 node

[steelhead31]

SLES12 is end of life ( although some customers can purchase extended support until October 2027 ) , but given we have had numerous problems with this node, due to not having the correct repositories available without a commercial subscription, it carries some security risk also.

This O/S level is also not supported by the provider.

Replace test-marist-sles12-s390x-2:
With test-marist-sles15-s390x-3:

[steelhead31]

New node installed : testsles15s390x3 / 148.100.74.157

Prep work ( update system python to 3.12 ) also completed, prior to deployment of playbooks.

[steelhead31]

Tests to commission in progress : https://ci.adoptium.net/job/AQA_Test_Pipeline/647/

Only versions 11,17,21,25

[steelhead31]

New Node : https://ci.adoptium.net/computer/test%2Dmarist%2Dsles15%2Ds390x%2D3/

[steelhead31]

Extended Run : https://ci.adoptium.net/job/AQA_Test_Pipeline/648/