Bump stripe from 11.1.0 to 11.1.1 in /backend

Bumps [stripe](https://github.com/stripe/stripe-python) from 11.1.0 to 11.1.1.
- [Release notes](https://github.com/stripe/stripe-python/releases)
- [Changelog](https://github.com/stripe/stripe-python/blob/master/CHANGELOG.md)
- [Commits](stripe/stripe-python@v11.1.0...v11.1.1)

---
updated-dependencies:
- dependency-name: stripe
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>