Bump bootstrap from 4.6.0 to 5.1.1

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.6.0 to 5.1.1.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](https://github.com/twbs/bootstrap/compare/v4.6.0...v5.1.1

)

---
updated-dependencies:
- dependency-name: bootstrap
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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