Add Ruby 3.2, remove Ruby 2.6 in CI

Author: ChrisBr

.github/workflows/tests.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '2.6', '2.7', '3.0', '3.1' ]
+        ruby: [ '2.7', '3.0', '3.1', '3.2' ]
     steps:
       - uses: actions/checkout@v2
       - name: Set up Ruby ${{ matrix.ruby }}