Arm backend: relax tolerance for test_constant_pad_nd_vgf_quant

[rascani]

Summary

The VGF + INT8 quantized pipeline for constant_pad_nd hits the same randomized-input numerical drift the TOSA INT variant has been working around since MLETORCH-989: the test_data_suite uses unseeded torch.rand so unfortunate input draws produce a single-element max abs diff (~6e-3) that exceeds the default atol (~4e-3). Apply the same atol/rtol the TOSA INT variant uses (atol=0.005, rtol=0.01) so the VGF run shares the existing umbrella ticket rather than continuing to flake on the same underlying issue.

Authored with Claude Code.

Test plan

CI

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

[pytorch-bot]

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❌ 1 Awaiting Approval, 2 New Failures, 4 Unrelated Failures

As of commit 333a8db with merge base e84a418 ():

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

• periodic (gh)

NEW FAILURES - The following jobs have failed:

• pull / test-coreml-bc-macos (macos-m1-stable) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-multimodal-macos (gemma3-4b) / macos-job (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following jobs failed but was present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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