WIP: Set n_workers for vgf_fp and tosa_fp tests

Signed-off-by: Oscar Andersson <oscar.andersson@arm.com>
Change-Id: I3c0d5f6abb9a21373baa5b3e101286af1bdb053c

Author: oscarandersson8218

.ci/scripts/test_backend.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # All rights reserved.
-# Copyright 2025 Arm Limited and/or its affiliates.
+# Copyright 2025-2026 Arm Limited and/or its affiliates.
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
@@ -94,7 +94,12 @@ CMAKE_ARGS="$EXTRA_BUILD_ARGS" ${CONDA_RUN_CMD} $SETUP_SCRIPT --build-tool cmake
 GOLDEN_DIR="${ARTIFACT_DIR}/golden-artifacts"
 export GOLDEN_ARTIFACTS_DIR="${GOLDEN_DIR}"
 
+PYTEST_WORKERS="auto"
+if [[ "$SUITE" == "models" ]] && [[ "$FLOW" == "arm_tosa_fp" || "$FLOW" == "arm_vgf_fp" ]]; then
+    PYTEST_WORKERS="1"
+fi
+
 EXIT_CODE=0
-${CONDA_RUN_CMD} pytest -c /dev/null -n auto backends/test/suite/$SUITE/ -m flow_$FLOW --json-report --json-report-file="$REPORT_FILE" || EXIT_CODE=$?
+${CONDA_RUN_CMD} pytest -c /dev/null -n "$PYTEST_WORKERS" backends/test/suite/$SUITE/ -m flow_$FLOW --json-report --json-report-file="$REPORT_FILE" || EXIT_CODE=$?
 # 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