Arm backend: Fix mypy warnings in test_insert_int32_casts_after_...

[perheld]

Fix mypy warnings in
test_insert_int32_casts_after_int64_placeholders_pass.py about using Tensor instead of LongTensor.

Signed-off-by: per.held@arm.com
Change-Id: I73ba7b75a727f32a6f13dcf905eb7b133a30f2a6

[pytorch-bot]

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✅ You can merge normally! (6 Unrelated Failures)

As of commit 4e7503d with merge base d07a49a ():

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

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

• pull / test-binary-size-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-setup-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest / windows / windows-job (gh) (trunk failure)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

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