⬆️ Bump aiohttp from 3.6.1 to 3.7.4 in /backend/requirements

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.6.1 to 3.7.4.
- [Release notes](https://github.com/aio-libs/aiohttp/releases)
- [Changelog](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp@v3.6.1...v3.7.4)

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

backend/requirements/ci.txt

@@ -6,7 +6,7 @@
 #
 aiodns==2.0.0
     # via -r requirements/base.txt
-aiohttp==3.6.1
+aiohttp==3.7.4
     # via -r requirements/base.txt
 amqp==2.5.1
     # via