Fix a bug in TorchBench ondemand CI. (#67743)
Summary:
Use the main branch when TorchBench branch is not specified.
RUN_TORCHBENCH: soft_actor_critic
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67743
Reviewed By: seemethere
Differential Revision: D32142663
Pulled By: xuzhao9
fbshipit-source-id: 160227835543b8e55c970025073839bf0f03aa81
