Fix DISPLAY_BUILD_NUMBER

The dot was accidentally removed.

Bug: 353425495
Test: build
Change-Id: Id0c08f3c98d5b2f56e49180baf98bb8847f6bebd
diff --git a/scripts/gen_build_prop.py b/scripts/gen_build_prop.py
index 799e00b..9ea56cb 100644
--- a/scripts/gen_build_prop.py
+++ b/scripts/gen_build_prop.py
@@ -188,7 +188,7 @@
 
     # Dev. branches should have DISPLAY_BUILD_NUMBER set
     if config["DisplayBuildNumber"]:
-      print(f"ro.build.display.id?={config['BuildId']} {config['BuildNumber']} {config['BuildKeys']}")
+      print(f"ro.build.display.id?={config['BuildId']}.{config['BuildNumber']} {config['BuildKeys']}")
     else:
       print(f"ro.build.display.id?={config['BuildId']} {config['BuildKeys']}")
   else: