py: quote Python versions in Actions workflow

3.10 might be interpreted as a float, yielding 3.1.

Author: djc

.github/workflows/publish.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python: [3.8, 3.9, 3.10, 3.11]
+        python: ["3.8", "3.9", "3.10", "3.11"]
 
     runs-on: ${{ matrix.os }}
     environment: "Publish wheels"