Fix mycroft-core PR generation

[krisgesling]

Description

• Fixes PR #141
• Uses outputs to share data between jobs
• Uses new syntax for setting environment variable to share data between steps within the update-mycroft-core job
• Uses a dedicated bot account to create the PR's to minimize security risk of using a Personal Access Token within Github Secrets.

The longer story

The method I used to assign the VERSION environment variable has been deprecated due to a security vulnerability. This switches to the new syntax outlined here. Even with that change, the environment variable doesn't seem to be accessible between jobs, only between steps within the same job.

During my reading, I also discovered that PR's generated directly by Github Actions apparently cannot trigger other Github Actions. So the use of a 3rd account is a recommended way of working around this: https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#triggering-further-workflow-runs

How to test

See Action output here:

• All working and PR created
• If the VERSION variable doesn't get set we don't create a PR
• If we don't publish to PyPI then we don't create a PR

CLA

• [x] Yes

[krisgesling]

Just squashed the commits

[krisgesling]

Yeah I learned some useful things working through this, so figured I'd be coming back here in the future to work out what I did :laughing: