Bump httpx from 0.19.0 to 0.20.0 (#1101)

Bumps [httpx](https://github.com/encode/httpx) from 0.19.0 to 0.20.0.
- [Release notes](https://github.com/encode/httpx/releases)
- [Changelog](https://github.com/encode/httpx/blob/master/CHANGELOG.md)
- [Commits](encode/httpx@0.19.0...0.20.0)

---
updated-dependencies:
- dependency-name: httpx
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

poetry.lock

@@ -63,7 +63,7 @@ anyio = "^3.3"
 curio = "^1.5"
 trio = "^0.19"
 attrs = "^21.2"
-httpx = "^0.19"
+httpx = "^0.20"
 
 mypy = "^0.910"
 wemake-python-styleguide = "^0.15"