Bump httpx from 0.16.1 to 0.18.0

Bumps [httpx](https://github.com/encode/httpx) from 0.16.1 to 0.18.0.
- [Release notes](https://github.com/encode/httpx/releases)
- [Changelog](https://github.com/encode/httpx/blob/master/CHANGELOG.md)
- [Commits](encode/httpx@0.16.1...0.18.0)

Signed-off-by: dependabot[bot] <support@github.com>

test-requirements.txt

@@ -43,9 +43,9 @@ h11==0.12.0
     # via
     #   httpcore
     #   uvicorn
-httpcore==0.12.2
+httpcore==0.13.0
     # via httpx
-httpx==0.16.1
+httpx==0.18.0
     # via -r test-requirements.in
 idna==2.10
     # via