Update GitHub build from Java 16 to 17.

Update GitHub build from Java 17-EA to 18-EA but comment it (not there
yet).

Author: garydgregory

.github/workflows/maven.yml

@@ -24,11 +24,11 @@ jobs:
     continue-on-error: ${{ matrix.experimental }}
     strategy:
       matrix:
-        java: [ 8, 11, 16 ]
+        java: [ 8, 11, 17 ]
         experimental: [false]
-        include:
-          - java: 17-ea
-            experimental: true
+#        include:
+#          - java: 18-ea
+#            experimental: true
 
     steps:
     - uses: actions/checkout@v2.3.4