Update DEFAULT_RUNNER_LABELS to match current GitHub runners

[kfess]

Summary

This PR updates the DEFAULT_RUNNER_LABELS array to reflect the current GitHub Actions runner support status, improving the VSCode auto-completion experience for workflow authors.

Changes Made

Removed unsupported runners:

• ubuntu-18.04, ubuntu-20.04 (support ended April 2025)
• macos-10.15, macos-11, macos-12 (support ended)

Added current runners:

• ubuntu-22.04
• ubuntu-24.04
• windows-2025
• windows-11-arm
• macos-13, macos-14, macos-15
• ARM variants: ubuntu-22.04-arm, ubuntu-24.04-arm
• Large runners: macos-13-large, macos-14-large, macos-15-large, macos-latest-large
• XLarge runners: macos-13-xlarge, macos-14-xlarge, macos-15-xlarge, macos-latest-xlarge

Validation

I conducted comprehensive validation of all GitHub Actions runners. Full results are available:

• GitHub Actions Test Results
• Detailed Summary

Related Issue

Resolves: #183

References

• GitHub Documentation on Hosted Runners
• GitHub Runner Images Repository
• GitHub Partner Runner Images