Upgrade: Bump gulp-imagemin from 7.1.0 to 8.0.0

Bumps [gulp-imagemin](https://github.com/sindresorhus/gulp-imagemin) from 7.1.0 to 8.0.0.
- [Release notes](https://github.com/sindresorhus/gulp-imagemin/releases)
- [Commits](sindresorhus/gulp-imagemin@v7.1.0...v8.0.0)

---
updated-dependencies:
- dependency-name: gulp-imagemin
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Close: #998

Author: dependabot[bot]