Update httpx requirement from ~=0.26.0 to ~=0.27.0 (#539)

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

requirements_testing.txt

@@ -1,4 +1,4 @@
-httpx~=0.26.0
+httpx~=0.27.0
 pgtest~=1.3
 pytest~=7.4
 pytest-cov~=4.1