[CI] Bump used latest non-LTS Java: 19 -> 20 (networknt#688)

Java 19 is reached EOL.

Author: valfirst

.github/workflows/ci.yml

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