Cap nh3 version in tests for older PyPys

Author: domdfcoding

tests/requirements.txt

@@ -4,6 +4,7 @@ coverage-pyver-pragma>=0.2.1
 editables>=0.2
 importlib-metadata>=3.6.0
 iniconfig!=1.1.0,>=1.0.1
+nh3<=0.2.14; python_version < "3.9" and implementation_name == "pypy"
 pyproject-examples@ https://github.com/repo-helper/pyproject-examples/archive/refs/heads/master.zip
 pytest>=6.0.0
 pytest-cov>=2.8.1