Add manual test workflow to main

[willjasen]

Why

Aikidio scans only the main branch, so the test workflow change also needs to be present there.

Changes

• Add the test workflow to main with only a manual workflow_dispatch trigger.
• Do not run tests automatically on pushes.

Validation

• The workflow diff was checked against main.
• The full ./tailmox test suite passed on the originating change.

[willjasen]

Closing this mistaken workflow-only promotion PR; the requested promotion is PR #30.