Bump slim/slim from 4.14.0 to 4.15.1

Bumps [slim/slim](https://github.com/slimphp/Slim) from 4.14.0 to 4.15.1.
- [Release notes](https://github.com/slimphp/Slim/releases)
- [Changelog](https://github.com/slimphp/Slim/blob/4.x/CHANGELOG.md)
- [Commits](slimphp/Slim@4.14.0...4.15.1)

---
updated-dependencies:
- dependency-name: slim/slim
  dependency-version: 4.15.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]