test: test against PyPy 3.9

Author: Rogdham

.github/workflows/build.yml

@@ -20,6 +20,7 @@ jobs:
           - "pypy-3.6"
           - "pypy-3.7"
           - "pypy-3.8"
+          - "pypy-3.9"
     steps:
       - uses: actions/checkout@v2
       - name: Setup Python ${{ matrix.python }}

CHANGELOG.md

@@ -13,7 +13,7 @@ adheres to [Semantic Versioning](https://semver.org/).
 
 - Necessary code changes following dev dependency update: black, pytest
 - Refactor a descriptor following PEP 487
-- Add tests for CPython 3.11
+- Add tests for CPython 3.11 and PyPy 3.9
 - Use CPython 3.11 for misc. tests
 
 ## [0.4.0] - 2022-01-09