Bump amphp/http from 1.6.3 to 1.7.3 (#96)

Bumps [amphp/http](https://github.com/amphp/http) from 1.6.3 to 1.7.3.
- [Release notes](https://github.com/amphp/http/releases)
- [Commits](amphp/http@v1.6.3...v1.7.3)

---
updated-dependencies:
- dependency-name: amphp/http
  dependency-type: indirect
...

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