Remove pinning to ET commit for Zephyr CI job (pytorch#13388)

### Summary
Currently, the CI jobs responsible for running the Zephyr tests checkout
a past version of ExecuTorch, but runs install_executorch.sh with the
pinned pytorch commit. Ideally, we would resolve this with resolving the
cmake errors that arise from using the most up-to-date version of
executorch, but for now, we can just keep the ExecuTorch and PyTorch
checkouts consistent for CI. This should prevent the Zephyr CI tests
from failing spuriously on unrelated PRs.

### Test plan
[PLEASE REMOVE] How did you test this PR? Please write down any manual
commands you used and note down tests that you have written if
applicable.

---------

Co-authored-by: Siddartha Pothapragada <[email protected]>

Author: 2 people

.github/workflows/trunk.yml

@@ -98,7 +98,7 @@ jobs:
 
         # Run setup scripts for Arm FVP and Arm AOT Compilation
         cd $ZEPHYR_PROJ_ROOT/modules/lib/executorch
-        install_executorch "--use-pt-pinned-commit"
+        install_executorch
         .ci/scripts/setup-arm-baremetal-tools.sh --target-toolchain zephyr
         source examples/arm/ethos-u-scratch/setup_path.sh
         source $ZEPHYR_PROJ_ROOT/zephyr/zephyr-env.sh