[Bugfix] Fix failing GGUF models test

[Isotr0py]

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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Purpose

• Fix [CI Failure]: Quantized Models Test - models/quantization/test_gguf.py::test_models #22136

Test Plan

Test Result

(Optional) Documentation Update

[github-actions]

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[gemini-code-assist]

Code Review

This pull request addresses a bug concerning GGUF models that also function as speculator models. The core change is within the maybe_override_with_speculators_target_model function, which is updated to correctly handle local GGUF file paths. It now properly parses the model path to distinguish the model's parent directory from the GGUF filename, ensuring that PretrainedConfig.get_config_dict can locate and load the associated configuration files. This change aligns the GGUF handling with other parts of the codebase and appears to be a correct and targeted fix. I have reviewed the changes and found no issues of high or critical severity.

[DarkLight1337]

Thanks for fixing!