Test against Java 20 (stable)

Remove Java 19 (no longer maintained).

Author: acogoluegnes

.github/workflows/test-supported-java-versions.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        java: [ '8', '11', '17', '19', '20-ea', '21-ea' ]
+        java: [ '8', '11', '17', '20', '21-ea' ]
     name:  Test against Java ${{ matrix.java }}
     steps:
       - uses: actions/checkout@v3