Update httpx[http2] requirement from ==0.23.* to ==0.24.* (#20)

Updates the requirements on [httpx[http2]](https://github.com/encode/httpx) to permit the latest version.
- [Release notes](https://github.com/encode/httpx/releases)
- [Changelog](https://github.com/encode/httpx/blob/master/CHANGELOG.md)
- [Commits](encode/httpx@0.23.0...0.24.0)

---
updated-dependencies:
- dependency-name: httpx[http2]
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -1,4 +1,4 @@
 bitcart
-httpx[http2]==0.23.* # TODO: remove pin when 1.0 is out
+httpx[http2]==0.24.* # TODO: remove pin when 1.0 is out
 Jinja2
 RestrictedPython