Bump optimum-executorch pin to include PR pytorch#208 (pytorch#16927)

Bumping the pin to optimum-executorch to include
huggingface/optimum-executorch#208.

This fixes whisper metal CI jobs such as
https://github.com/pytorch/executorch/actions/runs/21416571328/job/61668433882

Author: larryliu0820

.ci/docker/ci_commit_pins/optimum-executorch.txt

@@ -1 +1 @@
-f8aa919593cc51301ade73a2ee5491582521ab80
+5bf1aeb587e9b1f3572b0bd60265c5dafd007b73

.ci/scripts/export_model_artifact.sh

@@ -181,6 +181,8 @@ fi
 DEVICE_ARG=""
 if [ "$DEVICE" = "cuda" ] || [ "$DEVICE" = "cuda-windows" ]; then
   DEVICE_ARG="--device cuda"
+elif [ "$DEVICE" = "metal" ]; then
+  DEVICE_ARG="--device mps"
 fi
 
 optimum-cli export executorch \