pin to avoid broken PyQt5

Author: gilesknap

setup.cfg

@@ -16,7 +16,7 @@ classifiers =
     Programming Language :: Python :: 3.10
 
 [options]
-python_requires = >=3.8
+python_requires = >=3.7
 packages = find:
 # =src is interpreted as {"": "src"}
 # as per recommendation here https://hynek.me/articles/testing-packaging/
@@ -33,7 +33,7 @@ install_requires =
     # dls-pmaclib @ https://github.com/DiamondLightSource/dls-pmac-lib/archive/refs/tags/3.0.0.zip
     dls-pmaclib >= 3.0.1-beta1
     numpy
-    pyqt5
+    pyqt5 == 5.15.7
     pythonqwt
     mock