CI: run on Python 3.10

Refs #294

Author: akx

.github/workflows/python-package.yml

@@ -24,6 +24,7 @@ jobs:
           - "3.7"
           - "3.8"
           - "3.9"
+          - "3.10"
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
@@ -51,7 +52,7 @@ jobs:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: "3.10"
     - uses: actions/cache@v2
       with:
         path: ~/.cache/pip