CI: Add Ruby 3.2 to test matrix

Ruby 3.2.0 has been released on 25 Dec 2022.

Author: amotl

.github/workflows/tests.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest, macos-latest ] # , windows-latest ]
-        ruby-version: [ "2.4", "2.5", "2.6", "2.7", "3.0", "3.1" ]
+        ruby-version: [ "2.4", "2.5", "2.6", "2.7", "3.0", "3.1", "3.2" ]
 
     name: Ruby ${{ matrix.ruby-version }} on OS ${{ matrix.os }}
     steps: