Unbreak CI (#15505)

pytest 7.4.0 was just released, and our CI on `master` is very red as a
result. Looks like we're using a private API that we shouldn't be:
#15501 (comment). For
now let's just pin to pytest <7.4.0.

https://pypi.org/project/pytest/7.4.0/

Author: AlexWaygood

Diff for: test-requirements.txt

@@ -12,7 +12,8 @@ pre-commit
 pre-commit-hooks==4.4.0
 psutil>=4.0
 # pytest 6.2.3 does not support Python 3.10
-pytest>=6.2.4
+# TODO: fix use of removed private APIs so we can use the latest pytest
+pytest>=6.2.4,<7.4.0
 pytest-xdist>=1.34.0
 pytest-forked>=1.3.0,<2.0.0
 pytest-cov>=2.10.0