Upgrade aiohttp from 3.13.3 to 3.14.1

[hugovk]

Dependabot claims aiohttp needs updating at https://github.com/python/release-tools/security/dependabot from affected versions <= 3.13.3 to patched 3.13.4, but when it tries to upgrade it, also claims:

No security update is needed as aiohttp is no longer vulnerable
Dependabot hasn't attempted to update aiohttp as it's no longer vulnerable.

Let's just upgrade it. I ran:

pip-compile --generate-hashes --output-file=requirements.txt requirements.in --upgrade-package aiohttp
pip-compile --generate-hashes --output-file=dev-requirements.txt dev-requirements.in --upgrade-package aiohttp

[ezio-melotti]

It would be good to figure out why dependabot is failing to create PRs for this (it only does for mypy-requirements) and fix that, but I'm the meanwhile we can keep doing it manually to ensure aiohttp is updated.