Bump webpack in /glean/tests/unit/platform/utils/webext/sample

Bumps [webpack](https://github.com/webpack/webpack) from 5.37.1 to 5.51.1.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v5.37.1...v5.51.1)

---
updated-dependencies:
- dependency-name: webpack
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]