Bump smallvec from 1.4.2 to 1.8.0 in /TriggersFrontend

Bumps [smallvec](https://github.com/servo/rust-smallvec) from 1.4.2 to 1.8.0.
- [Release notes](https://github.com/servo/rust-smallvec/releases)
- [Commits](servo/rust-smallvec@v1.4.2...v1.8.0)

---
updated-dependencies:
- dependency-name: smallvec
  dependency-type: indirect
...

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Author: dependabot[bot]