Arm backend: Fix test_nss.py (#20373)

Lock down used neural-graphics-model-gym.git to version v0.3.0

Signed-off-by: Zingo Andersen <Zingo.Andersen@arm.com>

Author: zingo

backends/arm/scripts/install_models_for_test.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# 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.
@@ -8,7 +8,8 @@ set -e
 pip install -r backends/arm/requirements-arm-models-test.txt
 
 # Install model gym repository
-git clone https://github.com/arm/neural-graphics-model-gym.git
+MODEL_GYM_REF="${MODEL_GYM_REF:-v0.3.0}"
+git clone --depth 1 --branch "$MODEL_GYM_REF" https://github.com/arm/neural-graphics-model-gym.git
 cd neural-graphics-model-gym
 # Remove model-converter installation from model-gym repository (to prevent overwriting executorch version)
 if [[ "$(uname)" == "Darwin" ]]; then
@@ -18,4 +19,4 @@ else
 fi
 pip install . --no-deps
 cd ..
-rm -rf neural-graphics-model-gym
+rm -rf neural-graphics-model-gym