Try direct dependency on version of setuptools that patches:

 DeprecatedInstaller: setuptools.installer and fetch_build_eggs are deprecated

requirements.dev.txt

@@ -17,6 +17,7 @@ pytest-datadir==1.3.1     # via patientsearch (setup.py)
 pytest-flask==1.2.0       # via patientsearch (setup.py)
 pytest-mock==3.6.1        # via patientsearch (setup.py)
 pytest==6.2.5             # via patientsearch (setup.py), pytest-datadir, pytest-mock
+setuptools>=58.2.0
 toml==0.10.2              # via pytest
 typing-extensions==3.10.0.2  # via importlib-metadata
 zipp==3.5.0               # via importlib-metadata