fix backend tokenizer args override: key mismatch
# What does this PR do?

Related to #10390

Turns out it was a simple key mismatch - leaving as draft for now just to see the results of the full test suites, but hopeful this will fix the main problem for the related issue.
I'm talking with @n1t0 soon to get a better sense of where it might make sense as well yes! Will update then<|||||>went looking for similar case with this regex `(\[|\()"do_lower_case`, found only one more: 7e42461

I think this is it, will move onto #10121 once this is merged<|||||>There does seem to be an issue remaining though, as the tests in the suite currently fail with:
```
=========================== short test summary info ============================
FAILED tests/test_tokenization_auto.py::AutoTokenizerTest::test_do_lower_case
=== 1 failed, 5143 passed, 2103 skipped, 2207 warnings in 266.40s (0:04:26) ====
```