Bump windows-service from 0.7.0 to 0.8.1 in /agent

Bumps [windows-service](https://github.com/mullvad/windows-service-rs) from 0.7.0 to 0.8.1.
- [Release notes](https://github.com/mullvad/windows-service-rs/releases)
- [Changelog](https://github.com/mullvad/windows-service-rs/blob/main/CHANGELOG.md)
- [Commits](https://github.com/mullvad/windows-service-rs/compare/v0.7.0...v0.8.1)

---
updated-dependencies:
- dependency-name: windows-service
  dependency-version: 0.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

agent/cairnobs-agent/Cargo.toml

@@ -46,7 +46,7 @@ windows = { version = "0.58", features = [
     "Win32_System_Diagnostics_Etw",
     "Win32_Security",
 ] }
-windows-service = "0.7"
+windows-service = "0.8"
 quick-xml = "0.41"
 
 [build-dependencies]