Bump underscore.string from 3.3.5 to 3.3.6 in /ee/server/services (#24498)

Bumps [underscore.string](https://github.com/epeli/underscore.string) from 3.3.5 to 3.3.6.
- [Release notes](https://github.com/epeli/underscore.string/releases)
- [Changelog](https://github.com/esamattis/underscore.string/blob/master/CHANGELOG.markdown)
- [Commits](https://github.com/epeli/underscore.string/compare/3.3.5...3.3.6

)

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

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