Fix stable-2.6 branch to ansible-core 2.18, update test python version to 3.12

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Description

• What is being changed?
  fix ansible-core to 2.18 as the stable-2.6 branch need not be tested with anything after 2.18 as it is not supported
  https://access.redhat.com/support/policy/updates/ansible-automation-platform <ref

• Why is this change needed?
  stable-2.6 is pulling in ansible-core 2.19 as of this PR and having unwanted failures due to all the templating updates.
  also updated to Python 3.12 for integration tests to supplement python version supported as stable 2.15 is already testing 3.11

• How does this change address the issue?

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test update
• Refactoring (no functional changes)
• Development environment change
• Configuration change

Self-Review Checklist

• I have performed a self-review of my code
• I have added relevant comments to complex code sections
• I have updated documentation where needed
• I have considered the security impact of these changes
• I have considered performance implications
• I have thought about error handling and edge cases
• I have tested the changes in my local environment

Testing Instructions

Prerequisites

Steps to Test

Expected Results

Additional Context

Required Actions

• Requires documentation updates
• Requires downstream repository changes
• Requires infrastructure/deployment changes
• Requires coordination with other teams
• Blocked by PR/MR: #XXX

Screenshots/Logs

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DVCS PR Check Results:

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