[Auto] Add mistral regex regression test (cluster-45081-3): merged 1 of 2 PRs

[evalstate]

Merged PRs:

• Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317: Merged cleanly; code fix was already present on origin/main via Fix Kimi-K2.5 tokenizer regression and _patch_mistral_regex AttributeError huggingface/transformers#45359, but this PR still adds a useful regression test for the mistral regex patch path.

Skipped PRs:

• fix AttributeError in _patch_mistral_regex huggingface/transformers#45086: Skipped after no-op merge attempt; its fix is already in origin/main and it adds no test coverage beyond Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317.

Failed PRs:

• None.

Notes:

• Verified current branch is merge-cluster-cluster-45081-3-20260423223633 in the target repo.
• Cluster contains issue _patch_mistral_regex crashes with AttributeError: 'tokenizers.Tokenizer' object has no attribute 'backend_tokenizer' when loading Mistral tokenizer with fix_mistral_regex=True huggingface/transformers#45081 and PRs fix AttributeError in _patch_mistral_regex huggingface/transformers#45086 and Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317.
• Issue _patch_mistral_regex crashes with AttributeError: 'tokenizers.Tokenizer' object has no attribute 'backend_tokenizer' when loading Mistral tokenizer with fix_mistral_regex=True huggingface/transformers#45081 is still open.
• origin/main already contains the underlying bugfix in commit 282078b from PR Fix Kimi-K2.5 tokenizer regression and _patch_mistral_regex AttributeError huggingface/transformers#45359.
• Local merge of Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317 produced merge commit 0c3185b and the effective diff versus origin/main is only the added regression test in tests/models/auto/test_tokenization_auto.py.
• Attempted targeted pytest run, but the environment lacks a working local test setup: repo venv has no pytest and external pytest run failed due to missing safetensors.
• Repo was left on the requested branch with no merge in progress; pre-existing untracked agent/log files were left untouched.

Next steps:

• If desired, run the targeted tokenizer tests in a fully provisioned environment to validate the added regression test.
• Treat fix AttributeError in _patch_mistral_regex huggingface/transformers#45086 as superseded by main/Fix Kimi-K2.5 tokenizer regression and _patch_mistral_regex AttributeError huggingface/transformers#45359 and prefer only the regression-test delta from Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317.

[evalstate]

Trace for this mergeability run: https://huggingface.co/datasets/evalstate/transformers-merge-experiments/blob/main/2604232357-ItQ6EO__dev__codex.jsonl