Fix IP Adapter Support for SAG Pipeline

[stephen-iezzi]

What does this PR do?

Addresses part of #7064 by updating the IP adapter support for the SAG pipeline

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Who can review?

@yiyixuxu

[yiyixuxu]

thanks!
can we add IPAdapterTesterMixin to the fast test here

diffusers/tests/pipelines/stable_diffusion_sag/test_stable_diffusion_sag.py

Line 41 in e3cd6ca

class StableDiffusionSAGPipelineFastTests(PipelineLatentTesterMixin, PipelineTesterMixin, unittest.TestCase):

similar to what's done in this PR #6862

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[stephen-iezzi]

Added the tests!