Add pypy support

Author: Kyle-Verhoog

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "pypy-3.6"]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2