Bump slim/psr7 from 1.2.0 to 1.6.1 in /php-slim

Bumps [slim/psr7](https://github.com/slimphp/Slim-Psr7) from 1.2.0 to 1.6.1.
- [Release notes](https://github.com/slimphp/Slim-Psr7/releases)
- [Commits](slimphp/Slim-Psr7@1.2.0...1.6.1)

---
updated-dependencies:
- dependency-name: slim/psr7
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]