chore: Upgrade to Flow 24.3.0.alpha1

Author: mshabarov

versions.json

@@ -102,7 +102,7 @@
             "npmName": "@vaadin/field-highlighter"
         },
         "flow": {
-            "javaVersion": "24.3-SNAPSHOT"
+            "javaVersion": "24.3.0.alpha1"
         },
         "flow-cdi": {
             "javaVersion": "15.0.1"