chore(deps): bump @tootallnate/once and @google-cloud/spanner (#2002)

Removes [@tootallnate/once](https://github.com/TooTallNate/once). It's no longer used after updating ancestor dependency [@google-cloud/spanner](https://github.com/googleapis/nodejs-spanner). These dependencies need to be updated together.


Removes `@tootallnate/once`

Updates `@google-cloud/spanner` from 7.21.0 to 8.6.0
- [Release notes](https://github.com/googleapis/nodejs-spanner/releases)
- [Changelog](https://github.com/googleapis/nodejs-spanner/blob/main/CHANGELOG.md)
- [Commits](googleapis/nodejs-spanner@v7.21.0...v8.6.0)

---
updated-dependencies:
- dependency-name: "@tootallnate/once"
  dependency-version: 
  dependency-type: indirect
- dependency-name: "@google-cloud/spanner"
  dependency-version: 8.6.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]