CI: Test on Python 3.10, build packages in Python 3.10

Author: effigies

.github/workflows/package.yml

@@ -21,7 +21,7 @@ jobs:
       matrix:
         include:
           - os: ubuntu-latest
-            python-version: 3.8
+            python-version: "3.10"
     steps:
       - uses: actions/checkout@v2
         with:

.github/workflows/pre-release.yml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-latest', 'macos-latest']
-        python-version: [3.8, 3.9]
+        python-version: [3.8, 3.9, "3.10"]
         install: ['pip']
         check: ['ci_tests']
         pip-flags: ['PRE_PIP_FLAGS']

.github/workflows/stable.yml

@@ -26,7 +26,7 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-latest', 'macos-latest']
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
         install: ['pip']
         check: ['ci_tests']
         pip-flags: ['']