Fix retry variable on mac (#19333)

Author: JacobSzwejbka

.ci/scripts/test_backend.sh

@@ -97,6 +97,11 @@ GOLDEN_DIR="${ARTIFACT_DIR}/golden-artifacts"
 export GOLDEN_ARTIFACTS_DIR="${GOLDEN_DIR}"
 
 EXIT_CODE=0
-${CONDA_RUN_CMD} pytest -c /dev/null -n auto "${PYTEST_RETRY_ARGS[@]}" backends/test/suite/$SUITE/ -m flow_$FLOW --json-report --json-report-file="$REPORT_FILE" || EXIT_CODE=$?
+PYTEST_ARGS=(-c /dev/null -n auto)
+if [[ ${#PYTEST_RETRY_ARGS[@]} -gt 0 ]]; then
+    PYTEST_ARGS+=("${PYTEST_RETRY_ARGS[@]}")
+fi
+PYTEST_ARGS+=("backends/test/suite/$SUITE/" -m "flow_$FLOW" --json-report --json-report-file="$REPORT_FILE")
+${CONDA_RUN_CMD} pytest "${PYTEST_ARGS[@]}" || EXIT_CODE=$?
 # Generate markdown summary.
 ${CONDA_RUN_CMD} python -m executorch.backends.test.suite.generate_markdown_summary_json "$REPORT_FILE" > ${GITHUB_STEP_SUMMARY:-"step_summary.md"} --exit-code $EXIT_CODE