Arm backend: Shorten input names passed to the FVP

[gggekov]

Modify the backends/arm/test/runner_utils.py so that we pass relative paths to the FVP. This is to allow us get around the 256 char limit on the FVP and enables testing of the slice operator for 16x8. Solves internal ticket MLETORCH-1403.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

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❌ 2 New Failures, 1 Cancelled Job

As of commit 51974d9 with merge base 0e18b9f ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 1c84ce80bb0b9c517d4b02d0355c156819f5fa7d3b6a3ad051c955c002a45eac /exec failed with exit code 1
• trunk / test-mcu-models (cmake) / linux-job (gh)
  RuntimeError: Command docker exec -t 5cc1a402bfdd1f7fa843d98732d55c0260b0f9ce2037d1bd513354eec33b45e3 /exec failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• trunk / test-models-macos-cpu (emformer_join, xnnpack-quantization-delegation) / macos-job (gh)
  ##[error]The operation was canceled.

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