Update go.mod

change from 1.25 to 1.23

Author: derrickaw

learning/tour-of-beam/backend/go.mod

@@ -15,7 +15,7 @@
 
 module beam.apache.org/learning/tour-of-beam/backend
 
-go 1.25.0
+go 1.23.0
 
 require (
 	github.com/GoogleCloudPlatform/functions-framework-go v1.5.3