Update flow to 24.4.0.alpha1 (#4871)

Author: vaadin-bot

versions.json

@@ -102,7 +102,7 @@
             "npmName": "@vaadin/field-highlighter"
         },
         "flow": {
-            "javaVersion": "24.4-SNAPSHOT"
+            "javaVersion": "24.4.0.alpha1"
         },
         "flow-cdi": {
             "javaVersion": "15.0.1"