[#23828] docdb: Fix compile error in lwproto-test.cc

Summary:
D37548 / a28b3ec changed protobuf_message_total_bytes_limit to uint32, but a new declaration was added in lwproto-test.cc between test run and land, causing the following compile error:
```
[2024-09-06T21:57:51.729Z] ld.lld: error: undefined symbol: fLI::FLAGS_protobuf_message_total_bytes_limit
[2024-09-06T21:57:51.729Z] >>> referenced by dynamic_annotations.h:686 (../../src/yb/gutil/dynamic_annotations.h:686)
[2024-09-06T21:57:51.729Z] >>>               src/yb/rpc/CMakeFiles/lwproto-test.dir/lwproto-test.cc.o:(yb::rpc::LWProtoTest_BigMessage_Test::TestBody())
[2024-09-06T21:57:51.729Z] >>> did you mean: fLU::FLAGS_protobuf_message_total_bytes_limit
[2024-09-06T21:57:51.729Z] >>> defined in: lib/libyb_util.so
[2024-09-06T21:57:51.729Z] clang++: error: linker command failed with exit code 1 (use -v to see invocation)
```

This diff fixes the compile error.
Jira: DB-12730

Test Plan: Jenkins: urgent, compile only

Reviewers: hsunder

Reviewed By: hsunder

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D37869

src/yb/rpc/lwproto-test.cc

@@ -23,7 +23,7 @@
 #include "yb/util/size_literals.h"
 #include "yb/util/test_macros.h"
 
-DECLARE_int32(protobuf_message_total_bytes_limit);
+DECLARE_uint32(protobuf_message_total_bytes_limit);
 DECLARE_uint64(rpc_max_message_size);
 
 namespace yb {