gha: only run jobs when events are for 'sopel-irc' owned repos

[HumorBaby]

Description

As of right now, the GitHub Actions CI workflow will run on forks too.
This PR checks the workflow context to see if events are for the 'sopel-irc' owner, and only runs jobs if so. This check can/should be moved/updated as new jobs are defined, or if the event/branch filter for the CI workflow changes.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches¹

¹As best as possible. Confirmed that adding this prevents from running on my fork.

[dgw]

You don't think needs: tests will block the Coveralls finisher from running without a condition?

Presumably the pypi.yml workflow will fail because of the missing secret, but maybe it should also have this condition.

I can't believe there's no way to specify a condition for an entire workflow… Putting it on every job is ridiculous.

[dgw]

Really, I just want to merge this and further refine it later if needed. My question(s) above can be answered regardless of whether the PR remains unmerged. 😄

[dgw]

Update: Workflow runs are still created on a fork; they just immediately skip the job. Better than before, though still not ideal.

A true fix probably would have to come from the GitHub Actions team modifying this (asinine) default behavior to be more like a typical CI service—most of which seem to simply ignore forks.