compiler: Update java_plugin.cpp to support Edition 2026 (grpc#12931)

Author: JasonLunn

compiler/src/java_plugin/cpp/java_plugin.cpp

@@ -58,7 +58,9 @@ class JavaGrpcGenerator : public protobuf::compiler::CodeGenerator {
     return protobuf::Edition::EDITION_PROTO2;
   }
   protobuf::Edition GetMaximumEdition() const override {
-#if GOOGLE_PROTOBUF_VERSION >= 6032000
+#if GOOGLE_PROTOBUF_VERSION >= 6036000
+    return protobuf::Edition::EDITION_2026;
+#elif GOOGLE_PROTOBUF_VERSION >= 6032000
     return protobuf::Edition::EDITION_2024;
 #else
     return protobuf::Edition::EDITION_2023;