CI tests failing due to linking error in conda-based pytest #735
Description
When PR #693 was merged, it started generating an error in the conda-based pytest GitHub action. The error occurs when importing scipy:
from scipy.signal import tf2zpk, zpk2tf, cont2discrete
[17](https://github.com/python-control/python-control/runs/6637792716#step:5:18)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/signal/__init__.py:309: in <module>
[18](https://github.com/python-control/python-control/runs/6637792716#step:5:19)
from . import _sigtools, windows
[19](https://github.com/python-control/python-control/runs/6637792716#step:5:20)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/signal/windows/__init__.py:41: in <module>
[20](https://github.com/python-control/python-control/runs/6637792716#step:5:21)
from ._windows import *
[21](https://github.com/python-control/python-control/runs/6637792716#step:5:22)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/signal/windows/_windows.py:7: in <module>
[22](https://github.com/python-control/python-control/runs/6637792716#step:5:23)
from scipy import linalg, special, fft as sp_fft
[23](https://github.com/python-control/python-control/runs/6637792716#step:5:24)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/fft/__init__.py:91: in <module>
[24](https://github.com/python-control/python-control/runs/6637792716#step:5:25)
from ._helper import next_fast_len
[25](https://github.com/python-control/python-control/runs/6637792716#step:5:26)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/fft/_helper.py:3: in <module>
[26](https://github.com/python-control/python-control/runs/6637792716#step:5:27)
from ._pocketfft import helper as _helper
[27](https://github.com/python-control/python-control/runs/6637792716#step:5:28)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/fft/_pocketfft/__init__.py:3: in <module>
[28](https://github.com/python-control/python-control/runs/6637792716#step:5:29)
from .basic import *
[29](https://github.com/python-control/python-control/runs/6637792716#step:5:30)
/usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/fft/_pocketfft/basic.py:6: in <module>
[30](https://github.com/python-control/python-control/runs/6637792716#step:5:31)
from . import pypocketfft as pfft
[31](https://github.com/python-control/python-control/runs/6637792716#step:5:32)
E ImportError: /usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/linalg/../../../../libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /usr/share/miniconda/envs/test-environment/lib/python3.9/site-packages/scipy/fft/_pocketfft/pypocketfft.cpython-39-x86_64-linux-gnu.so)
Other CI tests are working, so it is probably something in the way that we are managing dependencies in the GitHub action scripts.