fix(deps): Update the Java code generator (gapic-generator-java) to 2.40.0

PiperOrigin-RevId: 630403028
diff --git a/WORKSPACE b/WORKSPACE
index cd6b9cd..18d6f71 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -263,7 +263,7 @@
     ],
 )
 
-_gapic_generator_java_version = "2.39.0"
+_gapic_generator_java_version = "2.40.0"
 
 maven_install(
     artifacts = [