Add Java 28-ea to GH CI as an experimental build.

Author: garydgregory

.github/workflows/maven.yml

@@ -37,8 +37,8 @@ jobs:
         include:
             - java: 27-ea
               experimental: true
-#            - java: 27-ea
-#              experimental: true
+            - java: 28-ea
+              experimental: true
 
     steps:
     - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1