Current coverage for aiohttp_requests has some gaps.

.nox/cover/lib/python3.7/site-packages/google/auth/transport/_aiohttp_requests.py 98 19 16 1 74%

• 57-58,
• 76-78,
• 81-90,
• 102,
• 106,
• 110,
• 114,
• 298->299,
• 299-301