Update httpx requirement from ~=0.26.0 to ~=0.27.0

Updates the requirements on [httpx](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@0.26.0...0.27.0)

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

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

requirements.txt

@@ -6,4 +6,4 @@
 # versions and only increase the lower bound if necessary
 
 # httpx has no stable release yet, so let's be cautious for now
-httpx ~= 0.26.0
+httpx ~= 0.27.0