Tokenizer from_pretrained should not use local files named like token…
…izer files

This fixes the issue reported in #19488.
Basically, if a user has a local file in the working directory named like any of the files the tokenizer is looking for in `from_pretrained`, for instance `tokenizer.json`, that file is going to be used instead of the file in the repo/folder passed along. The added test fails on current main and is fixed by the PR.

Fixes #19488

_The documentation is not available anymore as the PR was closed or merged._