Bump grpcio from 1.67.1 to 1.68.0 in /spiffe (#259)

Bumps [grpcio](https://github.com/grpc/grpc) from 1.67.1 to 1.68.0.
- [Release notes](https://github.com/grpc/grpc/releases)
- [Changelog](https://github.com/grpc/grpc/blob/master/doc/grpc_release_schedule.md)
- [Commits](grpc/grpc@v1.67.1...v1.68.0)

---
updated-dependencies:
- dependency-name: grpcio
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>