solProtoFuzzer of OSSFUZZ can not generate different solidity program

## Description
I added code in [solProtoFuzzer.cpp](https://github.com/ethereum/solidity/tree/develop/test/tools/ossfuzz) to output the Solidity program each time, but I found that each outputted program is the same.

## Environment

- Compiler version: 0.8.25
- Target EVM version (as per compiler settings): None
- Framework/IDE (e.g. Truffle or Remix): None
- EVM execution environment / backend / blockchain client: None
- Operating system: Linux

## Steps to Reproduce

```cpp
DEFINE_PROTO_FUZZER(Program const& _input)
{
ProtoConverter converter;
string sol_source = converter.protoToSolidity(_input);

// ·········································································
auto now = std::chrono::system_clock::now();
std::time_t now_c = std::chrono::system_clock::to_time_t(now);
std::tm localTime = *std::localtime(&now_c);
std::ostringstream oss;
oss << std::put_time(&localTime, "%Y%m%d-%H%M%S");

std::hash hasher;
size_t hashValue = hasher(sol_source);
std::string hashString = std::to_string(hashValue);

std::string dump_path_string="/mnt/sdd1/solProtoFuzzer/"+hashString+"_"+oss.str()+".sol";
ofstream of(dump_path_string.c_str());
of.write(sol_source.data(), static_cast(sol_source.size()));
// ············································································
```
However, I found that all the generated programs are the same, as follows.

```solidity

pragma solidity >=0.0;

contract C {
function test() public returns (uint)
{
return 0;
}
}
```

Start in test/tools/ossfuzz/solProtoFuzzer.cpp, especially DEFINE_PROTO_FUZZER and the ProtoConverter::protoToSolidity call shown in the report. Reproduce the issue using the reported OSSFUZZ setup and inspect why different fuzz inputs produce the same Solidity source. Done means the fuzzer generates varied Solidity programs and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.