Bump middleman from 4.5.1 to 4.6.3

Bumps [middleman](https://github.com/middleman/middleman) from 4.5.1 to 4.6.3.
- [Changelog](https://github.com/middleman/middleman/blob/main/CHANGELOG.md)
- [Commits](https://github.com/middleman/middleman/commits)

---
updated-dependencies:
- dependency-name: middleman
  dependency-version: 4.6.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]