github ci: use 3.10 (without -dev)

.github/workflows/ci.yml

@@ -58,7 +58,7 @@ jobs:
               python-version: '3.9'
               toxenv: py39-fuse3
             - os: ubuntu-20.04
-              python-version: '3.10-dev'
+              python-version: '3.10'
               toxenv: py310-fuse3
             - os: macos-latest
               python-version: '3.8'