www/py-aiohttp: update to 3.7.4.post0

PR: 256219
Approved by: koobs (maintainer)
Security: CVE-2021-21330
Security: 3000acee-c45d-11eb-904f-14dae9d5a9d2
MFH: 2020Q2 (bugfix, security release(s))

(cherry picked from commit ac412b55156cc77c8e96fb631a338a617749bcb7)