Update test_stable.yml

.github/workflows/test_stable.yml

@@ -71,6 +71,7 @@ jobs:
         min_torch_version="$(if ${{ matrix.python-version == '3.12' }}; then echo "2.2.0"; else echo "${min_torch_version}"; fi)"
         min_gpytorch_version=$(grep '\bgpytorch[>=]=' ${req_txt} | sed 's/[^0-9.]//g')
         min_linear_operator_version=$(grep '\blinear_operator[>=]=' ${req_txt} | sed 's/[^0-9.]//g')
+        pip install "numpy<2"  # Numpy >2.0 is not compatible with PyTorch <2.2.
         pip install "torch==${min_torch_version}" "gpytorch==${min_gpytorch_version}" "linear_operator==${min_linear_operator_version}"
         pip install .[test]
     - name: Unit tests and coverage -- BoTorch