Ignore reuse_dist_env (#6623)
Tests with `reuse_dist_env = True` often causes memory leaks. This PR
ignores `reuse_dist_env` and forcibly sets it to `False`. This change
might slow down the tests, but I think it is better to manually restart
runners and relaunch tests.
Memory usages (See #6578):
- `reuse_dist_env == True`:
https://github.com/microsoft/DeepSpeed/actions/runs/11302940871/job/31439471512
- `reuse_dist_env == False`:
https://github.com/microsoft/DeepSpeed/actions/runs/11303250613/job/31440137894
