Use workflow dispatch for meta bump

[auscompgeek]

Right now we're using a repository dispatch to ping robotpy-meta. There's no reason to not be using a workflow dispatch instead to specifically target the bump workflow.

https://docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows#workflow_dispatch
https://docs.github.com/en/free-pro-team@latest/rest/reference/actions#create-a-workflow-dispatch-event

[virtuald]

... I think that's what we're using?

[auscompgeek]

No, we're definitely using repository dispatch currently:

https://github.com/robotpy/robotpy-meta/blob/8471c4b6b34c14188c4c46d0285dc665a553aa7c/.github/workflows/bump.yml#L4

(why on earth does that not generate a preview)

[auscompgeek]

GitHub blog post about workflow dispatch: https://github.blog/changelog/2020-07-06-github-actions-manual-triggers-with-workflow_dispatch/