Do not use shards for single run tests (#53883)
Summary:
Do not compute shards if whole testsuite needs to be run anyway.
Helps avoid occasional test duplication/gaps when access to test time database is not available while one of the shards is computed
Fixes https://github.com/pytorch/pytorch/issues/53882
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53883
Reviewed By: janeyx99
Differential Revision: D27005910
Pulled By: malfet
fbshipit-source-id: f9603db0523a3a2539118e3fec1c6874c54f8d6d
