⬆️ Expand aiohttp version range

A new version of aiohttp has been released, with [an important fix preventing header injection](aio-libs/aiohttp#4818). I looked through the aiohttp changelog and wasn't able to find any breaking changes, so I believe it should be safe to use with gql.

setup.py

@@ -36,7 +36,7 @@
 ] + tests_requires
 
 install_aiohttp_requires = [
-    "aiohttp>=3.7.1,<3.8.0",
+    "aiohttp>=3.7.1,<3.9.0",
 ]
 
 install_requests_requires = [