Bump aiohttp-session from 2.7.0 to 2.8.0

Bumps [aiohttp-session](https://github.com/aio-libs/aiohttp_session) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/aio-libs/aiohttp_session/releases)
- [Changelog](https://github.com/aio-libs/aiohttp-session/blob/master/CHANGES.txt)
- [Commits](aio-libs/aiohttp-session@v2.7.0...v2.8.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements-dev.txt

@@ -1,6 +1,6 @@
 aiohttp-jinja2==1.1.2
 aiohttp-security==0.4.0
-aiohttp-session==2.7.0
+aiohttp-session==2.8.0
 aiohttp==3.6.0
 aiomysql==0.0.20
 aiopg==0.16.0