GITHUB_TOKEN cannot push to fork repos in scheduled workflows.
Remove the GITHUB_TOKEN fallback so the workflow fails explicitly
when UPSTREAM_TOKEN is missing, instead of silently 403-ing.
Also add issues:write permission and git user config for merges.
Replace actions-cool/issues-helper and aormsby/Fork-Sync-With-Upstream-action
with native git commands and actions/github-script. This fixes the
'Repository access blocked' error caused by GitHub restricting access
to third-party actions in fork repositories.
Replace actions-cool/issues-helper and aormsby/Fork-Sync-With-Upstream-action
with native git commands and actions/github-script. This fixes the
'Repository access blocked' error caused by GitHub restricting access
to third-party actions in fork repositories.
