Two bugs introduced in #13009 found during acceptance testing:
1. `pr create --assignee @copilot` sent the literal `@copilot` to the
API because NewIssueState only ran MeReplacer on assignees, not
CopilotReplacer. Fixed by switching to SpecialAssigneeReplacer (which
handles both @me and @copilot) like issue create already does.
2. The replaceActorsForAssignable mutation requires the [bot] suffix on
bot actor logins (e.g. `copilot-swe-agent[bot]`), unlike
requestReviewsByLogin which has a separate botLogins field. Added the
suffix in ReplaceActorsForAssignableByLogin for CopilotAssigneeLogin.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
bff468bafe