Bugfix: Add initializer to model in AttentionMask directly

[jambayk]

Description

Fixes a bug introduced in PR #17427 where self.add_initializer is called in AttentionMask but the class doesn't have the given method.

This adds the initializer directly to self.model as before but with raw=False as intended in the PR above.

Motivation and Context

Fixes the bug described above.
The bug was caught while running Olive tests with the latest ort-nightly builds.
https://dev.azure.com/aiinfra/PublicPackages/_build/results?buildId=360918&view=logs&j=dbbdd4d8-ffd3-515a-31fd-659375dbdff8&t=13dad60e-7187-5e88-dbc0-776ed0850a3f&l=601

[jambayk]

@tianleiwu FYI

[jambayk]

@tianleiwu can you please trigger the required pipelines using /azp run commands?
I am not a contributor on the repository so they don’t get triggered automatically.

I don’t also have merge permissions for when the required checks are complete.
Thanks!

[baijumeswani]

/azp run Linux CPU CI Pipeline, Linux CPU Minimal Build E2E CI Pipeline, Linux GPU CI Pipeline, Linux GPU TensorRT CI Pipeline, Linux OpenVINO CI Pipeline, MacOS CI Pipeline, ONNX Runtime Web CI Pipeline, onnxruntime-binary-size-checks-ci-pipeline, Linux QNN CI Pipeline

[baijumeswani]

/azp run Windows CPU CI Pipeline, Windows GPU CI Pipeline, Windows GPU TensorRT CI Pipeline, Windows ARM64 QNN CI Pipeline, orttraining-linux-ci-pipeline, orttraining-linux-gpu-ci-pipeline, orttraining-ortmodule-distributed, ONNX Runtime React Native CI Pipeline Windows x64 QNN CI Pipeline

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[tianleiwu]

/azp run Windows x64 QNN CI Pipeline

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).