Fix CogView3 lazy export to match the actual output class name

[rumitvn]

The cogview3 package advertises CogView3PlusPipelineOutput in its lazy _import_structure, but the output class is defined as CogView3PipelineOutput (no "Plus") in pipeline_output.py. Because of the mismatch, from diffusers.pipelines.cogview3 import CogView3PlusPipelineOutput raises an ImportError.

This points the lazy export at the real class name. The pipeline module already imports CogView3PipelineOutput, and the API docs autodoc that same name, so this just brings the lazy export in line with both.

# before: raises ImportError
from diffusers.pipelines.cogview3 import CogView3PlusPipelineOutput
# after: resolves to the class defined in pipeline_output.py
from diffusers.pipelines.cogview3 import CogView3PipelineOutput

The neighbouring CogView3PlusPipeline export is the actual pipeline class name and is intentionally left as-is — only the output-class export had the stray "Plus".

Addresses Issue 1 of #13648.

[github-actions]

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