chore: Update vaadin-testbench javaVersion to 10.2.0-alpha1 (#8743)

Co-authored-by: Zhe Sun <31067185+ZheSun88@users.noreply.github.com>

Author: mshabarov

versions.json

@@ -527,7 +527,7 @@
             "pro": true
         },
         "vaadin-testbench": {
-            "javaVersion": "10.1.0",
+            "javaVersion": "10.2.0-alpha1",
             "pro": true
         }
     }