NXP backend: Fix passing env to executor cmd

[roman-janik-nxp]

Summary

Fix of passing current env to subprocess call in execute_cmd(). Previous state where new env with 1 varible was passed prevented some tools from working correctly when call through subprocess call.

Test plan

Test for NXP executor runner.

cc @robert-kalmar

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19063

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• Rolling out OSDC (ARC) runners on pull & trunk workflows in PyTorch main

❌ 3 New Failures, 1 Cancelled Job, 2 Unrelated Failures

As of commit 36f787c with merge base c48ea12 ():

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-wheel-packages-linux (3.10) / linux-job (gh)
  RuntimeError: Command docker exec -t bf3fb09bd59763b5c69d69ec96c105e1ef10737e534d3cfbfb09d3a7f7ce5269 /exec failed with exit code 92
• pull / test-qnn-wheel-packages-linux (3.11) / linux-job (gh)
  RuntimeError: Command docker exec -t de665a6e7b819f2e91cd26e776b4c62f91dc5cc4319e5249ca6828fcb4f02a3f /exec failed with exit code 92
• pull / unittest-editable / macos / macos-job (gh)
  Library not loaded: @rpath/liblz4.1.dylib

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

• pull / unittest-buck / macos / macos-job (gh)
  ##[error]The operation was canceled.

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

• pull / unittest / windows / windows-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.

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

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

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

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[roman-janik-nxp]

The failing checks seem unrelated and the internal build passed. Merging.