Add UniLoraConfig to ALL_CONFIG_CLASSES test matrix

[DaoyuanLi2816]

What does this PR do?

UniLoraConfig (added in #3257) is missing from ALL_CONFIG_CLASSES in tests/test_config.py, so it isn't covered by the config test matrix (to_dict / save_pretrained / from_pretrained / from_json_file, copy/pickle, etc.).

This is the same kind of gap that #3365 addressed for CPTConfig/RandLoraConfig (and the four others I added there). UniLoraConfig landed afterwards without being registered. It's a public PeftConfig subclass with no mandatory init kwargs, so it's added as (UniLoraConfig, {}), consistent with the other entries.

I re-checked the full matrix against every public PeftConfig/PromptLearningConfig subclass — UniLoraConfig is the only one currently missing.

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