[Deepspeed] getting multiple prints of: Avoid using `tokenizers` before the fork if possible
on master when running with DeepSpeed I started getting multiple dumps of:
```
huggingface/tokenizers: The current process just got forked, after parallelism has already been used. Disabling parallelism to avoid deadlocks...
To disable this warning, you can either:
        - Avoid using `tokenizers` before the fork if possible
        - Explicitly set the environment variable TOKENIZERS_PARALLELISM=(true | false)
```
This script:
```
export BS=16; rm -r output_dir; PYTHONPATH=src USE_TF=0 CUDA_VISIBLE_DEVICES=0,1 deepspeed --num_gpus=2 examples/seq2seq/run_seq2seq.py --model_name_or_path t5-small --output_dir output_dir --adam_eps 1e-06 --do_eval --do_train --do_predict --evaluation_strategy=steps  --label_smoothing 0.1 --learning_rate 3e-5 --logging_first_step --logging_steps 1000 --max_source_length 128 --max_target_length 128 --num_train_epochs 1 --overwrite_output_dir --per_device_eval_batch_size $BS --per_device_train_batch_size $BS --predict_with_generate --eval_steps 25000  --sortish_sampler --task translation_en_to_ro  --val_max_target_length 128 --warmup_steps 500 --max_train_samples 100 --max_val_samples 100 --max_test_samples 100 --dataset_name wmt16 --dataset_config ro-en  --source_prefix "translate English to Romanian: " --deepspeed examples/tests/deepspeed/ds_config.json
```
prints it 15 times.

There are no 15 forks, it probably gets triggered by threads. The problem doesn't happen with DDP or DP.

Thank you.

@LysandreJik, @n1t0 

@chrissyjsartt, you probably accidentally subscribed/set to "Watching" the transformers repository which will now send you every comment on every Issue or PR. 

So urgently go to https://github.com/watching and "Unwatch" this or any other repositories you may have set to Watch. Then you will stop getting these notifications.<|||||>@LysandreJik replied elsewhere to set `TOKENIZERS_PARALLELISM=false` and to read https://github.com/huggingface/tokenizers/issues/187#issuecomment-635692450 for the explanation of why this is needed.

But this could make things slow, so trying `=true` first is a better idea - if it doesn't hang then all is good.

Also Anthony shared:
> If the `tokenizer` wasn't used to encode before forking the process, it shouldn't happen. So just a new `encode_batch` somewhere before the fork happens can be enough to trigger this.