In particular, this brings two important changes:
- rather than opening a new PR every time it runs, it uses a stable
branch name updating its content instead; this means that at most
there is one open PR per target branch
- a new secret "OPENAPI_SPEC_PR_REVIEW_TEAM" is introduced to specify
the name of the github team to notify when creating new PRs; this
helps to make sure that PRs are reviewed
