chore(deps): bump cloud.google.com/go/spanner from 1.70.0 to 1.73.0

Bumps [cloud.google.com/go/spanner](https://github.com/googleapis/google-cloud-go) from 1.70.0 to 1.73.0.
- [Release notes](https://github.com/googleapis/google-cloud-go/releases)
- [Changelog](https://github.com/googleapis/google-cloud-go/blob/main/CHANGES.md)
- [Commits](googleapis/google-cloud-go@spanner/v1.70.0...spanner/v1.73.0)

---
updated-dependencies:
- dependency-name: cloud.google.com/go/spanner
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>