Fix pypi-publish workflow to handle manual triggers

[Copilot]

The pypi-publish.yml workflow failed when manually triggered via workflow_dispatch because it unconditionally referenced github.event.workflow_run, which only exists for workflow_run triggers.

Changes

• test-testpypi-installation job: Added github.event_name != 'workflow_dispatch' guard to skip TestPyPI verification when manually triggered (package won't exist yet)
• build job: Added always() condition with explicit result checks to run when test job succeeds or is skipped, but not when failed
• checkout step: Made ref conditional to use github.event.workflow_run.head_sha for workflow_run events and github.ref for manual triggers

Behavior

workflow_run trigger: Test TestPyPI installation → Build → Publish to PyPI
workflow_dispatch trigger: Skip test → Build → Publish to PyPI

# Before
if: ${{ github.event.workflow_run.conclusion == 'success' }}

# After  
if: ${{ github.event_name != 'workflow_dispatch' && github.event.workflow_run.conclusion == 'success' }}

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