chore: Add aiohttp requirements test constraint. (#1566)

See https://github.com/googleapis/google-auth-library-python/issues/1565
for more information.

Author: clundin25

system_tests/secrets.tar.enc

@@ -17,4 +17,4 @@ grpcio
 pytest-asyncio; python_version > '3.0'
 aioresponses; python_version > '3.0'
 asynctest; python_version > '3.0'
-aiohttp; python_version > '3.0'
+aiohttp < 3.10.0; python_version > '3.0'