[CI] Pin aiohttp version to fix master branch

[simon-mo]

Why are these changes needed?

aiohttp 3.8.0 release broke our tests.

Traceback (most recent call last):
  File "/ray/python/ray/_private/services.py", line 1262, in start_dashboard
    import ray.dashboard.optional_deps  # noqa: F401
  File "/ray/python/ray/dashboard/optional_deps.py", line 8, in <module>
    import aiohttp.signals
ModuleNotFoundError: No module named 'aiohttp.signals'

ping for now, going to fix it soon.

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[simon-mo]

i'll merge after confirming it works. ETA 30min

[edoakes]

@simon-mo looks like it's still failing.

[fishbone]

@simon-mo I suspect it might be related to buildkite change. When I run the docker image locally, the failed tests actually passed

[simon-mo]

missed a file, the version was still 3.8.0 in some tests.

[jjyao]

Is it possible that we have a central place for defining aiohttp dependency?

[WangTaoTheTonic]

nice fix!