Fix tokenize endpoint

[njhill]

Fixes to the tokenization endpoint, missed during recent LoRA-related fixes.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 62.96%. Comparing base (fc6d899) to head (0efa312).

Files	Patch %	Lines
src/vllm_tgis_adapter/grpc/validation.py	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #54      +/-   ##
==========================================
- Coverage   63.03%   62.96%   -0.07%     
==========================================
  Files          18       18              
  Lines        1285     1288       +3     
  Branches      228      229       +1     
==========================================
+ Hits          810      811       +1     
- Misses        398      399       +1     
- Partials       77       78       +1     

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