Bump `autorebase.yml` to `v1.8` (#37584)

Summary:
`cirrus-actions/rebase` `v.1.8` fixes number of bugs.
`v1.8` Changelog: https://github.com/cirrus-actions/rebase/releases/tag/1.8
See: https://github.com/cirrus-actions/rebase

## Changelog:

[GENERAL] [SECURITY] - [Actions] Bump `autorebase.yml` to `v1.8`

Pull Request resolved: https://github.com/facebook/react-native/pull/37584

Test Plan: - `/rebase` comment should rebase the PR as usual.

Reviewed By: rshest

Differential Revision: D46264711

Pulled By: cipolleschi

fbshipit-source-id: 49974e5c1841c0af3637cf5bdbcde9e79ea0e671