Update httpcore requirement from <0.17.0,>=0.15.0 to >=0.15.0,<0.18.0 (#2642)

Update httpcore requirement from <0.17.0,>=0.15.0 to >=0.15.0,<0.18.0 (#2642)

Updates the requirements on [httpcore](https://github.com/encode/httpcore) to permit the latest version.
- [Release notes](https://github.com/encode/httpcore/releases)
- [Changelog](https://github.com/encode/httpcore/blob/master/CHANGELOG.md)
- [Commits](https://github.com/encode/httpcore/compare/0.15.0...0.17.0)

---
updated-dependencies:
- dependency-name: httpcore
  dependency-type: direct:production
...

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