Fix the wrong sample-rate of random tokens
# What does this PR do?
Fix the wrong sample-rate of random tokens from `0.1` to `0.5` in the `DataCollatorForLanguageModeling` and `DataCollatorForWholeWordMask`.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_17377). All of your documentation changes will be reflected on that endpoint.<|||||>Hello! Why is it wrong?<|||||>> Hello! Why is it wrong?

Sorry for late! we should replace 10% masked input tokens with random word, but the code means replacing 10% from the remaining tokens not replaced with [MASK] token. So, we only replace 0.2 * 0.1 tokens, it should be 0.2 * 0.5 ?!<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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