remove java 20 build in favor of LTS versions only

Author: barnhill

.github/workflows/gradle.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ '11', '17', '20', '21' ]
+        java: [ '11', '17', '21' ]
 
     environment: build
     steps: