Standard weekly patch release

[1.4.1] - 2021-08-03

• Fixed trainer.fit_loop.split_idx always returning None (#8601)
• Fixed references for ResultCollection.extra (#8622)
• Fixed reference issues during epoch end result collection (#8621)
• Fixed horovod auto-detection when horovod is not installed and the launcher is mpirun (#8610)
• Fixed an issue with training_step outputs not getting collected correctly for training_epoch_end (#8613)
• Fixed distributed types support for CPUs (#8667)
• Fixed a deadlock issue with DDP and torchelastic (#8655)
• Fixed accelerator=ddp choice for CPU (#8645)

Contributors

@awaelchli, @Borda, @carmocca, @kaushikb11, @tchaton

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