chore: Enable manually triggering main workflow in main branch

[vgarciabnz]

Adds the workflow_dispatch modifier to the main workflow, so it can be manually run if needed. The workflow_dispatch will only work in the main branch.

[superskip]

if: ${{ !contains(github.event.pull_request.title, '[skip publish]') }}

If you trigger the jobs with a workflow_dispatch event, then I suppose event.pull_request will be undefined, and this expression will throw. This could in turn mean the if-test will fail in this case?

[vgarciabnz]

Github actions seems to chain the undefined behavior so github.event.pull_request.title is just undefined if github.event.pull_request is undefined. It happens the same in the first step, with github.event.pull_request.merged == true.