Arm backend: Cast int64 buffers to int32

[AdrianLundell]

Cast int64 buffers using get_attr in the same way as regular placeholders.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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❌ 1 Awaiting Approval, 5 New Failures, 2 Pending

As of commit adf1213 with merge base 31118d7 ():

AWAITING APPROVAL - The following workflow needs approval before CI can run:

• periodic (gh)

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 46f3b8fc916d7aba6d0e5ded593ce50024dd1cb3059cac5afa08009450bf12ad /exec failed with exit code 1
• trunk / test-arm-backend-ethos-u (test_pytest_ops_ethos_u55) / linux-job (gh)
  RuntimeError: Command docker exec -t 5bb8b8905076adc9739cf8c3ea9742177e59711bc9975ffcb0cae86918cfad19 /exec failed with exit code 1
• trunk / test-arm-backend-ethos-u (test_pytest_ops_ethos_u85) / linux-job (gh)
  RuntimeError: Command docker exec -t 9006a8ab8f04617c66370c1dc34b1a702fc09453f06cce93435dbe32e1fe6737 /exec failed with exit code 1
• trunk / test-arm-backend-vkml (test_pytest_ops_vkml) / linux-job (gh)
  RuntimeError: Command docker exec -t 7a8002838d6f9e5f6419f3940c8b9dac355b6b96cc4ac92e17e51a6b01e4f910 /exec failed with exit code 1
• trunk / unittest-release / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn

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