[CI] Pin joblib to 1.2.0 in CI

[shrekris-anyscale]

Why are these changes needed?

test_joblib has been failing master over the past day:

Reverting the first PR that failed still doesn't fix the tests (see revert PR). The cause is likely that a new joblib version was released today (1.3.0), causing the test to start failing. Thanks @rkooo567 for catching this, and thanks @can-anyscale for giving pointers on what files to change.

This change pins joblib to 1.2.0 in the CI. It should fix test_joblib.

Related issue number

N/A

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• 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 added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• 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
    • test_joblib should start passing.

[rkooo567]

LGTM if tests pass. Also cc @matthewdeng for the follow-up (or lmk if you guys don't own this)

[shrekris-anyscale]

All tests pass.

@rkooo567 @matthewdeng this change is ready to merge.