Create PRs on other repos with GitHub CLI

Description of proposed changes

Motivation: move away from 3rd party Actions.

No functional change here except removal of the PR number from outputs (URL is more directly available and useful)

[x] Checks pass, but they don't actually test these changes
[x] ~If making user-facing changes, add a message in CHANGELOG.md summarizing the changes in this PR~ no functional changes
[x] Create preview PRs on downstream repositories (run)
[x] Preview PRs look good
[x] Job summary has PR links
[x] Running again updates existing PRs (run)
[x] Post-merge: remove peter-evans/create-pull-request from allow list in GitHub org settings (it was only used in this repo)