Check on and fix CI checks on spec repo

[Relequestual]

Action item from json-schema-org/community#200 - @jviotti

Our CI for this repo has not been running.
We should investigate what it was doing, define what we would like it to do, and (probably) resolve by using GitHub actions.

Related: #618

[Relequestual]

The merged PR did not work as expected.
@jviotti see https://github.com/json-schema-org/json-schema-spec/runs/7915793140?check_suite_focus=true#step:6:9

[Relequestual]

Julian fixed it. Woop!