[tests] Fix NougatModelIntegrationTest: pin artifact revision and update golden values (#48638)
- Pin nougat_pdf.png to revision ec57bf8c (file was removed from dataset
repo HEAD, causing 404 errors since 2025-06-20)
- Update expected logit slice and generation scores for fast image processor
- Update expected generated text (fast processor produces slightly different
pixel values, changing the generation output)
- Replace self.assertTrue(torch.allclose) with torch.testing.assert_close
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>