🧪 TESTS: Pin ipython<8 (#385)

ipython v8 is only available for Python 3.8+, and it changes exception text, which fails some regression tests

Author: chrisjsewell

setup.cfg

@@ -88,6 +88,8 @@ rtd =
 testing =
     coverage<5.0
     ipykernel~=5.5
+    # ipython v8 is only available for Python 3.8+, and it changes exception text
+    ipython<8
     jupytext~=1.11.2
     # TODO: 3.4.0 has some warnings that need to be fixed in the tests.
     matplotlib~=3.3.0