add java 21 to ci

Author: andre15silva

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        java-version: [ 8 , 11 , 16 , 18 ]
+        java-version: [ 8 , 11 , 16 , 18 , 20 ]
         compiler-version: [ 1.1 , 1.2 , 1.3 , 1.4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]
         os: [ ubuntu-latest , macos-latest , windows-latest ]