Recently, GitHub announced to deprecate the old way of handling required workflows:
Starting September 20th, 2023, users can configure their workflows using rulesets in order to run and pass in selected repositories before merging their code. On October 18th, users will no longer be able to access Actions Required Workflows and must use rulesets in its place.
This means, that since October 18th, required workflows are no longer working as expected.
/cc @travi
Related to: #625