Disable C extension in aiohttp to fix Python 3.12 install

Disable the C extension in aiohttp that's incompatible with Python 3.12
as of 3.8.5, in order to make it possible to install it (in pure Python
version) for testing.

tox.ini

@@ -81,3 +81,7 @@ passenv =
     AWS_ACCESS_KEY_ID
     AWS_DEFAULT_REGION
     AWS_SECRET_ACCESS_KEY
+setenv =
+    # workaround for broken C extension in aiohttp
+    # see: https://github.com/aio-libs/aiohttp/issues/7229
+    py312: AIOHTTP_NO_EXTENSIONS=1