Update test deps.

Author: taeold

tox.ini

@@ -24,11 +24,13 @@ envlist =
 usedevelop = true
 deps =
     docker
+    httpx
     pytest-asyncio
     pytest-cov
     pytest-integration
     pretend
-extras = async
+extras =
+    async
 setenv =
     PYTESTARGS = --cov=functions_framework --cov-branch --cov-report term-missing --cov-fail-under=100
     windows-latest: PYTESTARGS =
@@ -42,8 +44,6 @@ deps =
     isort
     mypy
     build
-extras =
-    async
 commands =
     black --check src tests conftest.py --exclude tests/test_functions/background_load_error/main.py
     isort -c src tests conftest.py