CI: Test on Python 3.10.0-rc1

Author: effigies

.github/workflows/pre-release.yml

@@ -26,7 +26,7 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-latest', 'windows-latest', 'macos-latest']
-        python-version: [3.8, 3.9]
+        python-version: ["3.8", "3.9", "3.10.0-rc.1"]
         architecture: ['x64', 'x86']
         install: ['setup']
         check: ['test']