[CICD] testpypi workflow add repository_dispatch trigger from llama-stack

[yanxi0830]

What does this PR do?

• add a workflow dispatch trigger for accepting repository_dispatch from llama-stack

Test Plan

• After merging to master, test with llama-stack workflow trigger

curl -L \
  -X POST \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer PAT_TOKEN" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  https://api.github.com/repos/meta-llama/llama-stack-client-python/dispatches \
  -d '{"event_type":"build-client-package","client_payload":{"source":"llama-stack-nightly", "version": "rc234"}}'

Sources

Please link relevant resources if necessary.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Ran pre-commit to handle lint / formatting issues.
• Read the contributor guideline,
  Pull Request section?
• Updated relevant documentation.
• Wrote necessary unit or integration tests.