Add GIT support to visual-question-answering pipeline

[DowellHd]

What does this PR do?

This PR adds GIT to the auto-model mapping for the visual-question-answering pipeline and updates the corresponding GIT pipeline test mapping.

This ensures that GIT models (e.g. GitForCausalLM) are correctly recognized and usable with the visual-question-answering pipeline, consistent with existing generative model support.

Issue

Partially addresses #21110

Tests

• pytest tests/models/git/test_modeling_git.py -v -k "pipeline" -x
• pytest tests/pipelines/test_pipelines_visual_question_answering.py -v -x

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Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline, Pull Request section?
• Was this discussed/approved via a Github issue or the forum?
  Issue reference: Add support for BLIP and GIT in image-to-text and VQA pipelines #21110
• Did you make sure to update the documentation with your changes?
  (Not required — registration/test-only change)
• Did you write any new necessary tests?
  (No new tests required; existing pipeline tests cover this change)

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Who can review?

@Rocketknight1

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: auto, git