allow reserved enums to be negative
https://github.com/protocolbuffers/upb/issues/1024

PiperOrigin-RevId: 494414605

python/google/protobuf/internal/descriptor_pool_test1.proto

diff --git a/python/google/protobuf/internal/descriptor_pool_test1.proto b/python/google/protobuf/internal/descriptor_pool_test1.proto
index f52e139..56d1cdd 100644
--- a/python/google/protobuf/internal/descriptor_pool_test1.proto
+++ b/python/google/protobuf/internal/descriptor_pool_test1.proto
@@ -85,6 +85,9 @@
       enum NestedEnum {
         LAMBDA = 11;
         MU = 12;
+
+        reserved -1;
+        reserved 536870913;  // 0x20000001
       }
       optional NestedEnum nested_enum = 1 [default = MU];
       optional string nested_field = 2 [default = "lambda"];